Optical surface identification for laser eye surgery

ABSTRACT

Systems and methods automatically locate optical surfaces of an eye and automatically generate surface models of the optical surfaces. A method includes OCT scanning of an eye. Returning portions of a sample beam are processed to locate a point on the optical surface and first locations on the optical surface within a first radial distance of the point. A first surface model of the optical surface is generated based on the location of the point and the first locations. Returning portions of the sample beam are processed so as to detect second locations on the optical surface beyond the first radial distance and within a second radial distance from the point. A second surface model of the optical surface is generated based on the location of the point on the optical surface and the first and second locations on the optical surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 14/070,245, filed on Nov. 1, 2013, which claims thebenefit of priority to U.S. Provisional Application No. 61/722,080,filed Nov. 2, 2012, all of which are herein incorporated by reference intheir entirety.

BACKGROUND

Cataract extraction is one of the most commonly performed surgicalprocedures in the world. A cataract is formed by opacification of thecrystalline lens or its envelope—the lens capsule—of the eye. Thecataract obstructs passage of light through the lens. A cataract canvary in degree from slight to complete opacity. Early in the developmentof an age-related cataract the power of the lens may be increased,causing near-sightedness (myopia). Gradual yellowing and opacificationof the lens may reduce the perception of blue colors as thosewavelengths are absorbed and scattered within the crystalline lens.Cataract formation typically progresses slowly resulting in progressivevision loss. Cataracts are potentially blinding if untreated.

A common cataract treatment involves replacing the opaque crystallinelens with an artificial intraocular lens (IOL). Presently, an estimated15 million cataract surgeries per year are performed worldwide. Thecataract treatment market is composed of various segments includingintraocular lenses for implantation, viscoelastic polymers to facilitatesurgical procedures, and disposable instrumentation including ultrasonicphacoemulsification tips, tubing, various knives, and forceps.

Presently, cataract surgery is typically performed using a techniquetermed phacoemulsification in which an ultrasonic tip with associatedirrigation and aspiration ports is used to sculpt the relatively hardnucleus of the lens to facilitate removal through an opening made in theanterior lens capsule. The nucleus of the lens is contained within anouter membrane of the lens that is referred to as the lens capsule.Access to the lens nucleus can be provided by performing an anteriorcapsulotomy in which a small (often round) hole is formed in theanterior side of the lens capsule. Access to the lens nucleus can alsobe provided by performing a manual continuous curvilinear capsulorhexis(CCC) procedure. After removal of the lens nucleus, a synthetic foldableintraocular lens (IOL) can be inserted into the remaining lens capsuleof the eye. Typically, the IOL is held in place by the edges of theanterior capsule and the capsular bag. The IOL may also be held by theposterior capsule, either alone or in unison with the anterior capsule.This latter configuration is known in the field as a “Bag-in-Lens”implant.

One of the most technically challenging and critical steps in thecataract extraction procedure is providing access to the lens nucleus.The manual continuous curvilinear capsulorhexis (CCC) procedure evolvedfrom an earlier technique termed can-opener capsulotomy in which a sharpneedle was used to perforate the anterior lens capsule in a circularfashion followed by the removal of a circular fragment of lens capsuletypically in the range of 5-8 mm in diameter. The smaller thecapsulotomy, the more difficult it is to produce manually. Thecapsulotomy provides access for the next step of nuclear sculpting byphacoemulsification. Due to a variety of complications associated withthe initial can-opener technique, attempts were made by leading expertsin the field to develop a better technique for removal of the circularfragment of the anterior lens capsule prior to the emulsification step.

The desired outcome of the manual continuous curvilinear capsulorhexisis to provide a smooth continuous circular opening through which notonly the phacoemulsification of the nucleus can be performed safely andeasily, but also to provide for easy insertion of the intraocular lens.The resulting opening in the anterior lens capsule provides access fortool insertion during removal of the nucleus and for IOL insertion, apermanent aperture for transmission of the image to the retina of thepatient, and also support of the IOL inside the remaining lens capsulethat limits the potential for dislocation. The resulting reliance on theshape, symmetry, uniformity, and strength of the remaining lens capsuleto contain, constrain, position, and maintain the IOL in the patient'seye limits the placement accuracy of the IOL, both initially and overtime. Subsequently, a patient's refractive outcome and resultant visualacuity are less deterministic and intrinsically sub-optimal due to theIOL placement uncertainty. This is especially true for astigmatismcorrecting (“toric”) and accommodating (“presbyopic”) IOLs.

Problems may also develop related to inability of the surgeon toadequately visualize the lens capsule due to lack of red reflex, tograsp the lens capsule with sufficient security, and to tear a smoothcircular opening in the lens capsule of the appropriate size and in thecorrect location without creating radial rips and extensions. Alsopresent are technical difficulties related to maintenance of the depthof the anterior chamber depth after opening the lens capsule, smallpupils, or the absence of a red reflex due to the lens opacity. Some ofthe problems with visualization can be minimized through the use of dyessuch as methylene blue or indocyanine green. Additional complicationsmay also arise in patients with weak zonules (typically older patients)and very young children that have very soft and elastic lens capsules,which are very difficult to controllably and reliably rupture and tear.

The implantation of a “Bag-in-Lens” IOL typically uses anterior andposterior openings in the lens capsule of the same size. Manuallycreating matching anterior and posterior capsulotomies for the“Bag-in-Lens” configuration, however, is particularly difficult.

Many cataract patients have astigmatic visual errors. Astigmatism canoccur when the corneal curvature is unequal in all directions. An IOLcan be used to correct for astigmatism but require precise rotationaland central placement. Additionally, IOLs are not typically used forcorrection beyond 5D of astigmatism. Many patients, however, haveastigmatic visual errors exceeding 5D. Higher correction beyond 5Dtypically requires reshaping the cornea to make it more spherical. Thereare numerous existing approaches for reshaping the cornea, includingCorneaplasty, Astigmatic Keratotomy, Corneal Relaxing Incision (CRI),and Limbal Relaxing Incision (LRI). In Astigmatic Keratotomy, CornealRelaxing Incision (CRI), and Limbal Relaxing Incision (LRI), cornealincisions are made in a well-defined manner and depth to allow thecornea to change shape to become more spherical. Presently, thesecorneal incisions are typically accomplished manually often with limitedprecision.

Thus, improved methods and systems for treating cataracts and/orcreating corneal incisions are needed.

SUMMARY

Methods and systems related to laser eye surgery are disclosed. A lasercan be used to form precise incisions in the cornea, in the lenscapsule, and/or in the crystalline lens nucleus. Structures of an eye,such as the cornea, the lens, the limbus, and the pupil can be measuredvia an efficient non-invasive scanning approach. Surface/curve modelsfor the measured structures (e.g., cornea anterior surface, corneaposterior surface, lens anterior surface, lens posterior surface, iris,and limbus) can be automatically generated. The surface/curve models canbe checked relative to suitable values and/or value ranges. Compositeimages of the surface/curve models and the respective structure can bedisplayed to, for example, enable user verification of the accuracy ofthe surface/curve model relative to the corresponding structure of theeye. The methods and system disclosed thus provide for fast andefficient planning and control of laser eye surgery procedures that caninclude precise incisions in the cornea, in the lens capsule, and/or inthe crystalline lens nucleus.

Thus, in one aspect, a method is provided of identifying opticalsurfaces in a patient's eye for performing laser surgery on thepatient's eye. The eye includes a cornea having an anterior surface anda lens capsule having an anterior portion and a posterior portion. Themethod includes coupling the patient's eye to a laser eye surgery systemthat includes an optical coherence tomography (OCT) imaging subsystem.The OCT imaging subsystem includes a reference path length that isadjustable so that a distance from the laser eye surgery system to areal portion detection window of the OCT imaging subsystem isadjustable. The OCT imaging subsystem employs a detection beam having aplurality of wavelengths such that the real portion detection windowspans a range of distances relative to the laser eye surgery system. AnOCT sample beam is generated. The OCT sample beam is focused at aplurality of different locations within the patient's eye. The pluralityof different locations include at least two different distances from thelaser eye surgery system. The different distances define a depth rangeencompassing an expected variability of distance from the laser eyesurgery system to the corneal anterior surface, to the lens capsuleanterior portion, or to the lens capsule posterior portion. Returningportions of the sample beam focused at the plurality of differentlocations are processed to locate, relative to the laser eye surgerysystem, the corneal anterior surface, the lens capsule anterior portion,or the lens capsule posterior portion.

Variations of the method of identifying optical surfaces in a patient'seye for performing laser surgery on the patient's eye are provided. Forexample, the different locations can be positioned at least threedifferent distances from the laser eye surgery system. The differentlocations can be located at least four different distances from thelaser eye surgery system. The different locations can be positioned atleast five different distances from the laser eye surgery system. Thefive different distances can define four intervening separatingdistances of between 0.25 mm and 0.75 mm. At least one of the fourintervening separating distances can be between 0.4 mm and 0.6 mm. Thefocusing of the OCT sample beam at a plurality of different locationswithin the patient's eye can include scanning the OCT sample beam in apattern having a maximum transverse dimension of less than 2.0 mm for atleast two of the different distances. The pattern can have a maximumdimension of less than 1.2 mm for at least two of the differentdistances. The reference path length can be held constant during thefocusing of the OCT sample beam at a plurality of different locationswithin the patient's eye. A boundary surface within the detection windowcan divide the detection window into a real portion of the detectionwindow and an imaginary portion of the detection window. The detectionwindow imaginary portion can be disposed between the laser eye surgerysystem and the detection window real portion. Alternatively, thedetection window real portion can be disposed between the laser eyesurgery system and the detection window imaginary portion. The laser eyesurgery system can be configured to employ an interface lens assemblythat is removably mounted to the laser eye surgery system so as to bedisposed between the OCT imaging subsystem and the eye. The interfacelens assembly can include an interface lens having an anterior surfaceand a posterior surface. The method can include setting the referencepath length to position the detection window boundary surface betweenthe interface lens posterior surface and the corneal anterior surfacesuch that the interface lens posterior surface is closer to thedetection window boundary surface than the corneal anterior surface whenprocessing returning portions of the sample beam focused at theplurality of different locations to locate the corneal anterior surface.The method can include setting the reference path length to position thedetection window boundary surface between the interface lens posteriorsurface and the lens capsule anterior surface such that the interfacelens posterior surface is further from the detection window boundarysurface than the lens capsule anterior surface when processing returningportions of the sample beam focused at the plurality of differentlocations to locate the lens capsule anterior surface. The detectionwindow boundary surface can be positioned such that the cornea anteriorsurface is closer to the detection window boundary surface than the lenscapsule anterior surface when processing returning portions of thesample beam focused at the plurality of different locations to locatethe lens capsule anterior surface. The method can include setting thereference path length to position the lens capsule posterior surfacebetween the detection window boundary surface and the lens capsuleanterior surface when processing returning portions of the sample beamfocused at the plurality of different locations to locate the lenscapsule posterior surface. The method can include using the OCT imagingsystem to locate the interface lens posterior surface. The method caninclude using the OCT imaging system to locate the interface lensanterior surface. The laser eye surgery system can be configured toemploy an interface assembly that is removably mounted to the laser eyesurgery system so as to be disposed between the OCT imaging subsystemand the eye. The interface assembly can include two or more referencefeatures. The method can include using the OCT imaging subsystem tolocate the reference features relative to the laser eye surgery system;and comparing the OCT based locations of the reference features relativeto predetermined positions of the reference features to determine atleast one of that the interface assembly is properly mounted to thelaser eye surgery system, that the interface assembly is improperlymounted to the laser eye surgery system, that fluid is present in theinterface assembly, that fluid is missing from the interface assembly,an angular orientation of the interface assembly relative to the lasereye surgery system, or whether the interface assembly is coupled with aleft or a right eye of a patient. The interface assembly can include asuction ring assembly that is configured to be coupled with the eye andincludes the two or more reference features and an interface lensassembly that includes an interface lens and couples the suction ringassembly to the laser eye surgery system.

In another aspect, a method is provided for processing optical coherencetomography (OCT) data to generate a surface model of an optical surfaceof a patient's eye. The patient's eye has a cornea having an anteriorsurface and a lens capsule having an anterior portion and a posteriorportion. The method includes coupling the patient's eye to a laser eyesurgery system that includes optical coherence tomography (OCT) imagingsubsystem. The OCT imaging subsystem includes a reference path lengththat is adjustable so that a distance from the laser eye surgery systemto a real portion detection window of the OCT imaging subsystem isadjustable. The OCT imaging subsystem employs a detection beam having aplurality of wavelengths such that the real portion detection windowspans a range of distances relative to the laser eye surgery system. AnOCT sample beam is generated. Returning portions of the sample beam areprocessed to locate a point on the optical surface relative to the lasereye surgery system. The OCT sample beam is focused within the patient'seye with the length of the reference path set to position the realportion detection window based on the location of the point on theoptical surface such that the real portion detection window encompassesthe optical surface for all expected variations in spatial dispositionof the optical surface. Returning portions of the sample beam areprocessed so as to detect first locations on the optical surface withina first radial distance of the point on the optical surface. A firstsurface model of the optical surface is generated based on the locationof the point on the optical surface and the first locations on theoptical surface. Returning portions of the sample beam are processed soas to detect second locations on the optical surface beyond the firstradial distance and within a second radial distance from the point onthe optical surface. A second surface model of the optical surface isgenerated based on the location of the point on the optical surface andthe first and second locations on the optical surface.

Variations of the method for processing optical coherence tomography(OCT) data to generate a surface model of an optical surface of apatient's eye are provided. For example, the optical surface can be thecornea anterior surface, the lens capsule anterior portion, or the lenscapsule posterior portion. Processing returning portions of the samplebeam so as to detect second locations can include generating a searchvolume defined by a first upper limit surface and a first lower limitsurface. The first upper and lower limit surfaces can be offset from thefirst surface model on respective opposing sides of the first surfacemodel. Processing returning portions of the sample beam focused at theplurality of different locations so as to detect second locations can belimited to the search volume. The method can include processingreturning portions of the sample beam so as to detect third locations onthe optical surface beyond the second radial distance and within a thirdradial distance from the point on the optical surface. The method caninclude generating a third surface model of the optical surface based onthe location of the point on the optical surface and the first, second,and third locations on the optical surface. Processing returningportions of the sample beam so as to detect third locations can includegenerating a second search volume defined by a second upper limitsurface and a second lower limit surface. The second upper and lowerlimit surfaces can be offset from the second surface model on respectiveopposing sides of the second surface model. Processing returningportions of the sample beam focused at the plurality of differentlocations so as to detect third locations can be limited to the secondsearch volume. At least one of the first and second surface models canbe an ellipsoid surface model or a spherical surface model. The opticalsurface can be the lens capsule anterior portion. A boundary surfacewithin the detection window can divide the detection window into a realportion of the detection window and an imaginary portion of thedetection window. The detection window imaginary portion can be disposedbetween the laser eye surgery system and the detection window realportion. Alternatively, the detection window real portion can bedisposed between the laser eye surgery system and the detection windowimaginary portion. When the optical surface is the lens capsule anteriorsurface, the reference path length can be set to position the lenscapsule anterior surface between the detection window boundary surfaceand the laser eye surgery system. When the optical surface is the lenscapsule posterior surface, the reference path length can be set toposition the lens capsule posterior surface between the detection windowboundary surface and the laser eye surgery system. The method caninclude calculating a transverse distance between an apex of the opticalsurface and a central axis of the laser eye surgery system. The methodcan include comparing the calculated transverse distance to apredetermined acceptable transverse distance value. The method caninclude inhibiting treatment of the patient's eye if the calculatedtransverse distance exceeds the predetermined acceptable transversedistance value.

In another aspect, a method is provided for identifying optical surfacesin an eye for performing laser surgery on the eye. The eye includes acornea having anterior and posterior surfaces, a lens capsule havinganterior and posterior surfaces, an iris, a pupil, and a limbus. Themethod includes coupling the eye to a laser eye surgery system thatincludes an optical coherence tomography (OCT) imaging subsystem, theOCT imaging subsystem including a reference path length that isadjustable so that a distance from the laser eye surgery system to adetection window of the OCT imaging subsystem is adjustable, the OCTimaging subsystem employing a detection beam having a plurality ofwavelengths such that the detection window spans a range of distancesrelative to the laser eye surgery system; using the OCT imagingsubsystem to locate a centrally-located point on the lens capsuleanterior surface; directing an OCT sample beam into the eye with thereference path length set to position the detection window to encompassthe lens capsule anterior surface and the iris; processing returningportions of the sample beam to identify, relative to the laser eyesurgery system, a plurality of edge points within the detection window,each edge point being disposed on an optical surface; generating asurface model of the lens capsule anterior surface based on the locationof the centrally-located point on the lens capsule anterior surface anda subset of the edge points; selecting a subset of the edge points thatare offset from the surface model of the lens capsule anterior surface;and generating a surface model of the iris based on the subset of theedge points that are offset from the surface model of the lens capsuleanterior surface.

Variations of the method for identifying optical surfaces in an eye forperforming laser surgery on the eye are provided. For example, thesurface model of the iris can be an oriented plane. The method caninclude using the OCT imaging subsystem to generate a surface model ofthe cornea anterior surface; generating a curved-line intersectionbetween the iris surface model and the cornea anterior surface model;and using the curved-line intersection to represent the location of thelimbus. The method can include processing a video image of the eye toidentify the pupil by searching outwardly from a central location toidentify edges of the iris. The method can include generating acurved-line model of the pupil based on the video identified pupil andthe iris surface model.

In another aspect, a method is provided for generating a surface modelof a posterior surface of a cornea of an eye, the cornea having ananterior surface. The method includes coupling the eye to a laser eyesurgery system that includes an optical coherence tomography (OCT)imaging subsystem, the OCT imaging subsystem including a reference pathlength that is adjustable so that a distance from the laser eye surgerysystem to a detection window of the OCT imaging subsystem is adjustable,the OCT imaging subsystem employing a detection beam having a pluralityof wavelengths such that the detection window spans a range of distancesrelative to the laser eye surgery system; directing an OCT sample beaminto the eye with the reference path length set to position thedetection window to encompass the cornea; generating a search volumedefined by a first upper limit surface and a first lower limit surface,the first upper and lower limit surfaces being offset from a surfacemodel of the cornea anterior surface; and processing returning portionsof the OCT sample beam corresponding to the search volume to identifypoints located on the cornea posterior surface. In many embodiments, atleast one of the first upper and lower limit surfaces is a sphere, anellipsoid, or a conicoid.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 is a perspective view showing a laser eye surgery system, inaccordance with many embodiments.

FIG. 2 is a simplified block diagram showing a top level view of theconfiguration of a laser eye surgery system, in accordance with manyembodiments.

FIG. 3 is a simplified diagram illustrating the configuration of anoptical assembly of a laser eye surgery system, in accordance with manyembodiments.

FIG. 4 is a simplified schematic diagram illustrating structures thatcan be measured by a laser eye surgery system, in accordance with manyembodiments.

FIG. 5 is a simplified block diagram of acts of a method forautomatically generating surface models and curved line models thataccurately represent the spatial disposition of optical surfaces andstructures of the patient's eye relative to a laser eye surgery system,in accordance with many embodiments.

FIG. 6 is a simplified diagram illustrating aspects of an OCT scan usedto measure the location of an anterior surface of a patient interfacelens of a laser eye surgery system, in accordance with many embodiments.

FIG. 7 is a simplified diagram illustrating aspects of an OCT scan usedto measure the location of a posterior surface of a patient interfacelens of a laser eye surgery system, in accordance with many embodiments.

FIG. 8A is a cross-sectional view of a suction ring assembly having areference surface that is locatable by an OCT scan, in accordance withmany embodiments.

FIG. 8B illustrates OCT measured locations of the reference surface ofFIG. 8A when the suction ring has been correctly docked to a laser eyesurgery system, in accordance with many embodiments.

FIG. 8C illustrates OCT measured locations of the reference surface ofFIG. 8A when the suction ring has been incorrectly docked to a laser eyesurgery system, in accordance with many embodiments.

FIG. 8D illustrates OCT measured locations of the reference surface ofFIG. 8A when interface fluid is missing between a patient interface lensand a patient's eye, in accordance with many embodiments.

FIG. 8E illustrates a template matched to an OCT generated image of areference surface of the suction ring of FIG. 8A, in accordance withmany embodiments.

FIGS. 9A and 9B are simplified diagrams illustrating aspects of an OCTscan used to measure the location of an anterior surface of a cornea, inaccordance with many embodiments.

FIG. 9C illustrates an OCT scan pattern having multiple focus depths, inaccordance with many embodiments.

FIG. 10A illustrates OCT scan data generated using an OCT scan patternhaving multiple focus depths, in accordance with many embodiments.

FIG. 10B shows a view of the OCT scan data of FIG. 10A for one of thefocus depths.

FIG. 10C shows original OCT scan data for one focus depth for the OCTscan data of FIG. 10A.

FIG. 10D shows a convoluted image with Gaussian derivative for the OCTscan data of FIG. 10A, in accordance with many embodiments.

FIG. 10E shows a detected edge relative to the original OCT scan data ofFIG. 10C, in accordance with many embodiments.

FIGS. 11A through 11D are simplified diagrams illustrating aspects of anOCT scan used to measure the spatial disposition of a cornea, inaccordance with many embodiments.

FIGS. 12A and 12B are simplified diagrams illustrating aspects of an OCTscan used to measure the location of an anterior surface of a lens, inaccordance with many embodiments.

FIGS. 13A through 13D are simplified diagrams illustrating aspects of anOCT scan used to measure the spatial disposition of an anterior surfaceof a lens, in accordance with many embodiments.

FIGS. 14A and 14B are simplified diagrams illustrating aspects of an OCTscan used to measure the location of a posterior surface of a lens, inaccordance with many embodiments.

FIG. 15 is a simplified diagram illustrating aspects of an OCT scan usedto measure the spatial disposition of a posterior surface of a lens, inaccordance with many embodiments.

FIGS. 16A through 16D illustrate an iterative process for processing OCTscan data to identify locations on an optical surface, in accordancewith many embodiments.

FIG. 17A illustrates OCT scan generated points used to generate asurface model of an iris, in accordance with many embodiments.

FIG. 17B illustrates pupil and limbus models generated based on the OCTscan generated iris points of FIG. 17A, in accordance with manyembodiments.

FIG. 17C shows pupil and limbus locations overlaid on a video image aneye, in accordance with many embodiments.

FIG. 17D shows cornea anterior surface locations, iris locations, and acurved-line model of the limbus generated by intersecting a corneaanterior surface model fit to the cornea anterior surface locations andthe oriented plane fit to the iris locations, in accordance with manyembodiments.

FIGS. 18A and 18B show axial and sagittal cross-sectional compositeimages of an eye, respectively, the composite images includingcross-sections of surface models overlaid on OCT generatedcross-sectional images of the eye, in accordance with many embodiments.

FIG. 19 is a simplified schematic diagram illustrating operating aspectsof a spectrometer-based spectral domain OCT, in accordance with manyembodiments.

FIGS. 20 and 21 are simplified schematic diagrams illustratinggeneration of a mirror image artifact, in accordance with manyembodiments.

FIG. 22 shows a composite image of imaged structures of an eye, inaccordance with many embodiments.

FIG. 23 is a simplified block diagram showing a top level view of analternate configuration of the laser eye surgery system, in accordancewith many embodiments.

DETAILED DESCRIPTION

System Configuration

FIG. 1 shows a laser eye surgery system 2, in accordance with manyembodiments, operable to form precise incisions in the cornea, in thelens capsule, and/or in the crystalline lens nucleus. The system 2includes a main unit 4, a patient chair 6, a dual function footswitch 8,and a laser footswitch 10.

The main unit 4 includes many primary subsystems of the system 2. Forexample, externally visible subsystems include a touch-screen controlpanel 12, a patient interface assembly 14, patient interface vacuumconnections 16, a docking control keypad 18, a patient interface radiofrequency identification (RFID) reader 20, external connections 22(e.g., network, video output, footswitch, USB port, door interlock, andAC power), laser emission indicator 24, emergency laser stop button 26,key switch 28, and USB data ports 30.

The patient chair 6 includes a base 32, a patient support bed 34, aheadrest 36, a positioning mechanism, and a patient chair joystickcontrol 38 disposed on the headrest 36. The positioning controlmechanism is coupled between the base 32 and the patient support bed 34and headrest 36. The patient chair 6 is configured to be adjusted andoriented in three axes (x, y, and z) using the patient chair joystickcontrol 38. The headrest 36 and a restrain system (not shown, e.g., arestraint strap engaging the patient's forehead) stabilize the patient'shead during the procedure. The headrest 36 includes an adjustable necksupport to provide patient comfort and to reduce patient head movement.The headrest 36 is configured to be vertically adjustable to enableadjustment of the patient head position to provide patient comfort andto accommodate variation in patient head size.

The patient chair 6 allows for tilt articulation of the patient's legs,torso, and head using manual adjustments. The patient chair 6accommodates a patient load position, a suction ring capture position,and a patient treat position. In the patient load position, the chair 6is rotated out from under the main unit 4 with the patient chair back inan upright position and patient footrest in a lowered position. In thesuction ring capture position, the chair is rotated out from under themain unit 4 with the patient chair back in reclined position and patientfootrest in raised position. In the patient treat position, the chair isrotated under the main unit 4 with the patient chair back in reclinedposition and patient footrest in raised position.

The patient chair 6 is equipped with a “chair enable” feature to protectagainst unintended chair motion. The patient chair joystick 38 can beenabled in either of two ways. First, the patient chair joystick 38incorporates a “chair enable” button located on the top of the joystick.Control of the position of the patient chair 6 via the joystick 38 canbe enabled by continuously pressing the “chair enable” button.Alternately, the left foot switch 40 of the dual function footswitch 8can be continuously depressed to enable positional control of thepatient chair 6 via the joystick 38.

In many embodiments, the patient control joystick 38 is a proportionalcontroller. For example, moving the joystick a small amount can be usedto cause the chair to move slowly. Moving the joystick a large amountcan be used to cause the chair to move faster. Holding the joystick atits maximum travel limit can be used to cause the chair to move at themaximum chair speed. The available chair speed can be reduced as thepatient approaches the patient interface assembly 14.

The emergency stop button 26 can be pushed to stop emission of all laseroutput, release vacuum that couples the patient to the system 2, anddisable the patient chair 6. The stop button 26 is located on the systemfront panel, next to the key switch 28.

The key switch 28 can be used to enable the system 2. When in a standbyposition, the key can be removed and the system is disabled. When in aready position, the key enables power to the system 2.

The dual function footswitch 8 is a dual footswitch assembly thatincludes the left foot switch 40 and a right foot switch 42. The leftfoot switch 40 is the “chair enable” footswitch. The right footswitch 42is a “vacuum ON” footswitch that enables vacuum to secure a liquidoptics interface suction ring to the patient's eye. The laser footswitch10 is a shrouded footswitch that activates the treatment laser whendepressed while the system is enabled.

In many embodiments, the system 2 includes external communicationconnections. For example, the system 2 can include a network connection(e.g., an RJ45 network connection) for connecting the system 2 to anetwork. The network connection can be used to enable network printingof treatment reports, remote access to view system performance logs, andremote access to perform system diagnostics. The system 2 can include avideo output port (e.g., HDMI) that can be used to output video oftreatments performed by the system 2. The output video can be displayedon an external monitor for, for example, viewing by family membersand/or training. The output video can also be recorded for, for example,archival purposes. The system 2 can include one or more data outputports (e.g., USB) to, for example, enable export of treatment reports toa data storage device. The treatments reports stored on the data storagedevice can then be accessed at a later time for any suitable purposesuch as, for example, printing from an external computer in the casewhere the user without access to network based printing.

FIG. 2 shows a simplified block diagram of the system 2 coupled with apatient eye 43. The patient eye 43 comprises a cornea, a lens, and aniris. The iris defines a pupil of the eye 43 that may be used foralignment of eye 43 with system 2. The system 2 includes a cutting lasersubsystem 44, a ranging subsystem 46, an alignment guidance system 48,shared optics 50, a patient interface 52, control electronics 54, acontrol panel/GUI 56, user interface devices 58, and communication paths60. The control electronics 54 is operatively coupled via thecommunication paths 60 with the cutting laser subsystem 44, the rangingsubsystem 46, the alignment guidance subsystem 48, the shared optics 50,the patient interface 52, the control panel/GUI 56, and the userinterface devices 58.

In many embodiments, the cutting laser subsystem 44 incorporatesfemtosecond (FS) laser technology. By using femtosecond lasertechnology, a short duration (e.g., approximately 10⁻¹³ seconds induration) laser pulse (with energy level in the micro joule range) canbe delivered to a tightly focused point to disrupt tissue, therebysubstantially lowering the energy level required as compared to thelevel required for ultrasound fragmentation of the lens nucleus and ascompared to laser pulses having longer durations.

The cutting laser subsystem 44 can produce laser pulses having awavelength suitable to the configuration of the system 2. As anon-limiting example, the system 2 can be configured to use a cuttinglaser subsystem 44 that produces laser pulses having a wavelength from1020 nm to 1050 nm. For example, the cutting laser subsystem 44 can havea diode-pumped solid-state configuration with a 1030 (+/−5) nm centerwavelength.

The cutting laser subsystem 44 can include control and conditioningcomponents. For example, such control components can include componentssuch as a beam attenuator to control the energy of the laser pulse andthe average power of the pulse train, a fixed aperture to control thecross-sectional spatial extent of the beam containing the laser pulses,one or more power monitors to monitor the flux and repetition rate ofthe beam train and therefore the energy of the laser pulses, and ashutter to allow/block transmission of the laser pulses. Suchconditioning components can include an adjustable zoom assembly to adaptthe beam containing the laser pulses to the characteristics of thesystem 2 and a fixed optical relay to transfer the laser pulses over adistance while accommodating laser pulse beam positional and/ordirectional variability, thereby providing increased tolerance forcomponent variation.

The ranging subsystem 46 is configured to measure the spatialdisposition of eye structures in three dimensions. The measured eyestructures can include the anterior and posterior surfaces of thecornea, the anterior and posterior portions of the lens capsule, theiris, and the limbus. In many embodiments, the ranging subsystem 46utilizes optical coherence tomography (OCT) imaging. As a non-limitingexample, the system 2 can be configured to use an OCT imaging systememploying wavelengths from 780 nm to 970 nm. For example, the rangingsubsystem 46 can include an OCT imaging system that employs a broadspectrum of wavelengths from 810 nm to 850 nm. Such an OCT imagingsystem can employ a reference path length that is adjustable to adjustthe effective depth in the eye of the OCT measurement, thereby allowingthe measurement of system components including features of the patientinterface that lie anterior to the cornea of the eye and structures ofthe eye that range in depth from the anterior surface of the cornea tothe posterior portion of the lens capsule and beyond.

The alignment guidance subsystem 48 can include a laser diode or gaslaser that produces a laser beam used to align optical components of thesystem 2. The alignment guidance subsystem 48 can include LEDs or lasersthat produce a fixation light to assist in aligning and stabilizing thepatient's eye during docking and treatment. The alignment guidancesubsystem 48 can include a laser or LED light source and a detector tomonitor the alignment and stability of the actuators used to positionthe beam in X, Y, and Z. The alignment guidance subsystem 48 can includea video system that can be used to provide imaging of the patient's eyeto facilitate docking of the patient's eye 43 to the patient interface52. The imaging system provided by the video system can also be used todirect via the GUI the location of cuts. The imaging provided by thevideo system can additionally be used during the laser eye surgeryprocedure to monitor the progress of the procedure, to track movementsof the patient's eye 43 during the procedure, and to measure thelocation and size of structures of the eye such as the pupil and/orlimbus.

The shared optics 50 provides a common propagation path that is disposedbetween the patient interface 52 and each of the cutting laser subsystem44, the ranging subsystem 46, and the alignment guidance subsystem 48.In many embodiments, the shared optics 50 includes beam combiners toreceive the emission from the respective subsystem (e.g., the cuttinglaser subsystem 44, and the alignment guidance subsystem 48) andredirect the emission along the common propagation path to the patientinterface. In many embodiments, the shared optics 50 includes anobjective lens assembly that focuses each laser pulse into a focalpoint. In many embodiments, the shared optics 50 includes scanningmechanisms operable to scan the respective emission in three dimensions.For example, the shared optics can include an XY-scan mechanism(s) and aZ-scan mechanism. The XY-scan mechanism(s) can be used to scan therespective emission in two dimensions transverse to the propagationdirection of the respective emission. The Z-scan mechanism can be usedto vary the depth of the focal point within the eye 43. In manyembodiments, the scanning mechanisms are disposed between the laserdiode and the objective lens such that the scanning mechanisms are usedto scan the alignment laser beam produced by the laser diode. Incontrast, in many embodiments, the video system is disposed between thescanning mechanisms and the objective lens such that the scanningmechanisms do not affect the image obtained by the video system.

The patient interface 52 is used to restrain the position of thepatient's eye 43 relative to the system 2. In many embodiments, thepatient interface 52 employs a suction ring that is vacuum attached tothe patient's eye 43. The suction ring is then coupled with the patientinterface 52, for example, using vacuum to secure the suction ring tothe patient interface 52. In many embodiments, the patient interface 52includes an optically transmissive structure having a posterior surfacethat is displaced vertically from the anterior surface of the patient'scornea and a region of a suitable liquid (e.g., a sterile bufferedsaline solution (BSS) such as Alcon BSS (Alcon Part Number 351-55005-1)or equivalent) is disposed between and in contact with the posteriorsurface and the patient's cornea and forms part of a transmission pathbetween the shared optics 50 and the patient's eye 43. The opticallytransmissive structure may comprise a lens 96 having one or more curvedsurfaces. Alternatively, the patient interface 22 may comprise anoptically transmissive structure having one or more substantially flatsurfaces such as a parallel plate or wedge. In many embodiments, thepatient interface lens is disposable and can be replaced at any suitableinterval, such as before each eye treatment.

The control electronics 54 controls the operation of and can receiveinput from the cutting laser subsystem 44, the ranging subsystem 46, thealignment guidance subsystem 48, the patient interface 52, the controlpanel/GUI 56, and the user interface devices 58 via the communicationpaths 60. The communication paths 60 can be implemented in any suitableconfiguration, including any suitable shared or dedicated communicationpaths between the control electronics 54 and the respective systemcomponents.

The control electronics 54 can include any suitable components, such asone or more processor, one or more field-programmable gate array (FPGA),and one or more memory storage devices. In many embodiments, the controlelectronics 54 controls the control panel/GUI 56 to provide forpre-procedure planning according to user specified treatment parametersas well as to provide user control over the laser eye surgery procedure.

The control electronics 54 may comprise a processor/controller 55(referred to herein as a processor) that is used to perform calculationsrelated to system operation and provide control signals to the varioussystem elements. A computer readable medium 57 (also referred to as adatabase or a memory) is coupled to the processor 55 in order to storedata used by the processor and other system elements. The processor 55interacts with the other components of the system as described morefully throughout the present specification. In an embodiment, the memory57 can include a look up table that can be utilized to control one ormore components of the laser system as described herein.

The processor 55 can be a general purpose microprocessor configured toexecute instructions and data, such as a Pentium processor manufacturedby the Intel Corporation of Santa Clara, Calif. It can also be anApplication Specific Integrated Circuit (ASIC) that embodies at leastpart of the instructions for performing the method in accordance withthe embodiments of the present disclosure in software, firmware and/orhardware. As an example, such processors include dedicated circuitry,ASICs, combinatorial logic, other programmable processors, combinationsthereof, and the like.

The memory 57 can be local or distributed as appropriate to theparticular application. Memory 57 may include a number of memoriesincluding a main random access memory (RAM) for storage of instructionsand data during program execution and a read only memory (ROM) in whichfixed instructions are stored. Thus, memory 57 provides persistent(non-volatile) storage for program and data files, and may include ahard disk drive, flash memory, a floppy disk drive along with associatedremovable media, a Compact Disk Read Only Memory (CD-ROM) drive, anoptical drive, removable media cartridges, and other like storage media.

The user interface devices 58 can include any suitable user input devicesuitable to provide user input to the control electronics 54. Forexample, the user interface devices 58 can include devices such as, forexample, the dual function footswitch 8, the laser footswitch 10, thedocking control keypad 18, the patient interface radio frequencyidentification (RFID) reader 20, the emergency laser stop button 26, thekey switch 28, and the patient chair joystick control 38.

FIG. 3 is a simplified block diagram illustrating an assembly 62, inaccordance with many embodiments, that can be included in the system 2.The assembly 62 is a non-limiting example of suitable configurations andintegration of the cutting laser subsystem 44, the ranging subsystem 46,the alignment guidance subsystem 48, the shared optics 50, and thepatient interface 52. Other configurations and integration of thecutting laser subsystem 44, the ranging subsystem 46, the alignmentguidance subsystem 48, the shared optics 50, and the patient interface52 may be possible and may be apparent to a person of skill in the art.

The assembly 62 is operable to project and scan optical beams into thepatient's eye 43. The cutting laser subsystem 44 includes an ultrafast(UF) laser 64 (e.g., a femtosecond laser). Using the assembly 62,optical beams can be scanned in the patient's eye 43 in threedimensions: X, Y, Z. For example, short-pulsed laser light generated bythe UF laser 64 can be focused into eye tissue to produce dielectricbreakdown to cause photodisruption around the focal point (the focalzone), thereby rupturing the tissue in the vicinity of the photo-inducedplasma. In the assembly 62, the wavelength of the laser light can varybetween 800 nm to 1200 nm and the pulse width of the laser light canvary from 10 fs to 10000 fs. The pulse repetition frequency can alsovary from 10 kHz to 500 kHz. Safety limits with regard to unintendeddamage to non-targeted tissue bound the upper limit with regard torepetition rate and pulse energy. Threshold energy, time to complete theprocedure, and stability can bound the lower limit for pulse energy andrepetition rate. The peak power of the focused spot in the eye 43 andspecifically within the crystalline lens and the lens capsule of the eyeis sufficient to produce optical breakdown and initiate aplasma-mediated ablation process. Near-infrared wavelengths for thelaser light are preferred because linear optical absorption andscattering in biological tissue is reduced for near-infraredwavelengths. As an example, the laser 64 can be a repetitively pulsed1031 nm device that produces pulses with less than 600 fs duration at arepetition rate of 120 kHz (+/−5%) and individual pulse energy in the 1to 20 micro joule range.

The cutting laser subsystem 44 is controlled by the control electronics54 and the user, via the control panel/GUI 56 and the user interfacedevices 58, to create a laser pulse beam 66. The control panel/GUI 56 isused to set system operating parameters, process user input, displaygathered information such as images of ocular structures, and displayrepresentations of incisions to be formed in the patient's eye 43.

The generated laser pulse beam 66 proceeds through a zoom assembly 68.The laser pulse beam 66 may vary from unit to unit, particularly whenthe UF laser 64 may be obtained from different laser manufacturers. Forexample, the beam diameter of the laser pulse beam 66 may vary from unitto unit (e.g., by +/−20%). The beam may also vary with regard to beamquality, beam divergence, beam spatial circularity, and astigmatism. Inmany embodiments, the zoom assembly 68 is adjustable such that the laserpulse beam 66 exiting the zoom assembly 68 has consistent beam diameterand divergence unit to unit.

After exiting the zoom assembly 68, the laser pulse beam 66 proceedsthrough an attenuator 70. The attenuator 70 is used to adjust thetransmission of the laser beam and thereby the energy level of the laserpulses in the laser pulse beam 66. The attenuator 70 is controlled viathe control electronics 54.

After exiting the attenuator 70, the laser pulse beam 66 proceedsthrough an aperture 72. The aperture 72 sets the outer useful diameterof the laser pulse beam 66. In turn the zoom determines the size of thebeam at the aperture location and therefore the amount of light that istransmitted. The amount of transmitted light is bounded both high andlow. The upper is bounded by the requirement to achieve the highestnumerical aperture achievable in the eye. High NA promotes low thresholdenergies and greater safety margin for untargeted tissue. The lower isbound by the requirement for high optical throughput. Too muchtransmission loss in the system shortens the lifetime of the system asthe laser output and system degrades over time. Additionally,consistency in the transmission through this aperture promotes stabilityin determining optimum settings (and sharing of) for each procedure.Typically, to achieve optimal performance the transmission through thisaperture is set at between 88% to 92%.

After exiting the aperture 72, the laser pulse beam 66 proceeds throughtwo output pickoffs 74. Each output pickoff 74 can include a partiallyreflecting mirror to divert a portion of each laser pulse to arespective output monitor 76. Two output pickoffs 74 (e.g., a primaryand a secondary) and respective primary and secondary output monitors 76are used to provide redundancy in case of malfunction of the primaryoutput monitor 76.

After exiting the output pickoffs 74, the laser pulse beam 66 proceedsthrough a system-controlled shutter 78. The system-controlled shutter 78ensures on/off control of the laser pulse beam 66 for procedural andsafety reasons. The two output pickoffs precede the shutter allowing formonitoring of the beam power, energy, and repetition rate as apre-requisite for opening the shutter.

After exiting the system-controlled shutter 78, the optical beamproceeds through an optics relay telescope 80. The optics relaytelescope 80 propagates the laser pulse beam 66 over a distance whileaccommodating positional and/or directional variability of the laserpulse beam 66, thereby providing increased tolerance for componentvariation. As an example, the optical relay can be a keplerian afocaltelescope that relays an image of the aperture position to a conjugateposition near to the xy galvo mirror positions. In this way, theposition of the beam at the XY galvo location is invariant to changes inthe beams angle at the aperture position. Similarly the shutter does nothave to precede the relay and may follow after or be included within therelay.

After exiting the optics relay telescope 80, the laser pulse beam 66 istransmitted to the shared optics 50, which propagates the laser pulsebeam 66 to the patient interface 52. The laser pulse beam 66 is incidentupon a beam combiner 82, which reflects the laser pulse beam 66 whiletransmitting optical beams from the ranging subsystem 46 and thealignment guidance subsystem: AIM 48.

Following the beam combiner 82, the laser pulse beam 66 continuesthrough a Z-telescope 84, which is operable to scan focus position ofthe laser pulse beam 66 in the patient's eye 43 along the Z axis. Forexample, the Z-telescope 84 can include a Galilean telescope with twolens groups (each lens group includes one or more lenses). One of thelens groups moves along the Z axis about the collimation position of theZ-telescope 84. In this way, the focus position of the spot in thepatient's eye 43 moves along the Z axis. In general, there is arelationship between the motion of lens group and the motion of thefocus point. For example, the Z-telescope can have an approximate 2×beam expansion ratio and close to a 1:1 relationship of the movement ofthe lens group to the movement of the focus point. The exactrelationship between the motion of the lens and the motion of the focusin the Z axis of the eye coordinate system does not have to be a fixedlinear relationship. The motion can be nonlinear and directed via amodel or a calibration from measurement or a combination of both.Alternatively, the other lens group can be moved along the Z axis toadjust the position of the focus point along the Z axis. The Z-telescope84 functions as a Z-scan device for scanning the focus point of thelaser-pulse beam 66 in the patient's eye 43. The Z-telescope 84 can becontrolled automatically and dynamically by the control electronics 54and selected to be independent or to interplay with the X and Y scandevices described next.

After passing through the Z-telescope 84, the laser pulse beam 66 isincident upon an X-scan device 86, which is operable to scan the laserpulse beam 66 in the X direction, which is dominantly transverse to theZ axis and transverse to the direction of propagation of the laser pulsebeam 66. The X-scan device 86 is controlled by the control electronics54, and can include suitable components, such as a motor, galvanometer,or any other well known optic moving device. The relationship of themotion of the beam as a function of the motion of the X actuator doesnot have to be fixed or linear. Modeling or calibrated measurement ofthe relationship or a combination of both can be determined and used todirect the location of the beam.

After being directed by the X-scan device 86, the laser pulse beam 66 isincident upon a Y-scan device 88, which is operable to scan the laserpulse beam 66 in the Y direction, which is dominantly transverse to theX and Z axes. The Y-scan device 88 is controlled by the controlelectronics 54, and can include suitable components, such as a motor,galvanometer, or any other well known optic moving device. Therelationship of the motion of the beam as a function of the motion ofthe Y actuator does not have to be fixed or linear. Modeling orcalibrated measurement of the relationship or a combination of both canbe determined and used to direct the location of the beam.Alternatively, the functionality of the X-scan device 86 and the Y-scandevice 88 can be provided by an XY-scan device configured to scan thelaser pulse beam 66 in two dimensions transverse to the Z axis and thepropagation direction of the laser pulse beam 66. The X-scan and Y-scandevices 86, 88 change the resulting direction of the laser pulse beam66, causing lateral displacements of UF focus point located in thepatient's eye 43.

After being directed by the Y-scan device 88, the laser pulse beam 66passes through a beam combiner 90. The beam combiner 90 is configured totransmit the laser pulse beam 66 while reflecting optical beams to andfrom a video subsystem 92 of the alignment guidance subsystem 48.

After passing through the beam combiner 90, the laser pulse beam 66passes through an objective lens assembly 94. The objective lensassembly 94 can include one or more lenses. In many embodiments, theobjective lens assembly 94 includes multiple lenses. The complexity ofthe objective lens assembly 94 may be driven by the scan field size, thefocused spot size, the degree of telecentricity, the available workingdistance on both the proximal and distal sides of objective lensassembly 94, as well as the amount of aberration control.

After passing through the objective lens assembly 94, the laser pulsebeam 66 passes through the patient interface 52. As described above, inmany embodiments, the patient interface 52 includes a patient interfacelens 96 having a posterior surface that is displaced vertically from theanterior surface of the patient's cornea and a region of a suitableliquid (e.g., a sterile buffered saline solution (BSS) such as Alcon BSS(Alcon Part Number 351-55005-1) or equivalent) is disposed between andin contact with the posterior surface of the patient interface lens 96and the patient's cornea and forms part of an optical transmission pathbetween the shared optics 50 and the patient's eye 43.

The shared optics 50 under the control of the control electronics 54 canautomatically generate aiming, ranging, and treatment scan patterns.Such patterns can be comprised of a single spot of light, multiple spotsof light, a continuous pattern of light, multiple continuous patterns oflight, and/or any combination of these. In addition, the aiming pattern(using the aim beam 108 described below) need not be identical to thetreatment pattern (using the laser pulse beam 66), but can optionally beused to designate the boundaries of the treatment pattern to provideverification that the laser pulse beam 66 will be delivered only withinthe desired target area for patient safety. This can be done, forexample, by having the aiming pattern provide an outline of the intendedtreatment pattern. This way the spatial extent of the treatment patterncan be made known to the user, if not the exact locations of theindividual spots themselves, and the scanning thus optimized for speed,efficiency, and/or accuracy. The aiming pattern can also be made to beperceived as blinking in order to further enhance its visibility to theuser. Likewise, the ranging beam 102 need not be identical to thetreatment beam or pattern. The ranging beam needs only to be sufficientenough to identify targeted surfaces. These surfaces can include thecornea and the anterior and posterior surfaces of the lens and may beconsidered spheres with a single radius of curvature. Also the opticsshared by the alignment guidance: video subsystem does not have to beidentical to those shared by the treatment beam. The positioning andcharacter of the laser pulse beam 66 and/or the scan pattern the laserpulse beam 66 forms on the eye 43 may be further controlled by use of aninput device such as a joystick, or any other appropriate user inputdevice (e.g., control panel/GUI 56) to position the patient and/or theoptical system.

The control electronics 54 can be configured to target the targetedstructures in the eye 43 and ensure that the laser pulse beam 66 will befocused where appropriate and not unintentionally damage non-targetedtissue. Imaging modalities and techniques described herein, such asthose mentioned above, or ultrasound may be used to determine thelocation and measure the thickness of the lens and lens capsule toprovide greater precision to the laser focusing methods, including 2Dand 3D patterning. Laser focusing may also be accomplished by using oneor more methods including direct observation of an aiming beam, or otherknown ophthalmic or medical imaging modalities, such as those mentionedabove, and/or combinations thereof. Additionally the ranging subsystemsuch as an OCT can be used to detect features or aspects involved withthe patient interface. Features can include fiducials placed on thedocking structures and optical structures of the disposable lens such asthe location of the anterior and posterior surfaces.

In the embodiment of FIG. 3, the ranging subsystem 46 includes an OCTimaging device. Additionally or alternatively, imaging modalities otherthan OCT imaging can be used. An OCT scan of the eye can be used tomeasure the spatial disposition (e.g., three dimensional coordinatessuch as X, Y, and Z of points on boundaries) of structures of interestin the patient's eye 43. Such structure of interest can include, forexample, the anterior surface of the cornea, the posterior surface ofthe cornea, the anterior portion of the lens capsule, the posteriorportion of the lens capsule, the anterior surface of the crystallinelens, the posterior surface of the crystalline lens, the iris, thepupil, and/or the limbus. The spatial disposition of the structures ofinterest and/or of suitable matching geometric modeling such as surfacesand curves can be generated and/or used by the control electronics 54 toprogram and control the subsequent laser-assisted surgical procedure.The spatial disposition of the structures of interest and/or of suitablematching geometric modeling can also be used to determine a wide varietyof parameters related to the procedure such as, for example, the upperand lower axial limits of the focal planes used for cutting the lenscapsule and segmentation of the lens cortex and nucleus, and thethickness of the lens capsule among others. Additionally the rangingsubsystem such as an OCT can be used to detect features or aspectsinvolved with the patient interface. Features can include fiducialsplaced on the docking structures and optical structures of thedisposable lens such as the location of the anterior and posteriorsurfaces.

The ranging subsystem 46 in FIG. 3 includes an OCT light source anddetection device 98. The OCT light source and detection device 98includes a light source that generates and emits an OCT source beam witha suitable broad spectrum. For example, in many embodiments, the OCTlight source and detection device 98 generates and emits the OCT sourcebeam with a broad spectrum from 810 nm to 850 nm wavelength. Thegenerated and emitted light is coupled to the device 98 by a single modefiber optic connection.

The OCT source beam emitted from the OCT light source and detectiondevice 98 is passed through a pickoff/combiner assembly 100, whichdivides the OCT source beam into a sample beam 102 and a referenceportion 104. A significant portion of the sample beam 102 is transmittedthrough the shared optics 50. A relative small portion of the samplebeam is reflected from the patient interface 52 and/or the patient's eye43 and travels back through the shared optics 50, back through thepickoff/combiner assembly 100 and into the OCT light source anddetection device 98. The reference portion 104 is transmitted along areference path 106 having an adjustable path length. The reference path106 is configured to receive the reference portion 104 from thepickoff/combiner assembly 100, propagate the reference portion 104 overan adjustable path length, and then return the reference portion 106back to the pickoff/combiner assembly 100, which then directs thereturned reference portion 104 back to the OCT light source anddetection device 98. The OCT light source and detection device 98 thendirects the returning small portion of the sample beam 102 and thereturning reference portion 104 into a detection assembly, which employsa time domain detection technique, a frequency detection technique, or asingle point detection technique. For example, a frequency domaintechnique can be used with an OCT wavelength of 830 nm and bandwidth of100 nm.

Once combined with the UF laser pulse beam 66 subsequent to the beamcombiner 82, the OCT sample beam 102 follows a shared path with the UFlaser pulse beam 66 through the shared optics 50 and the patientinterface 52. In this way, the OCT sample beam 102 is generallyindicative of the location of the UF laser pulse beam 66. Similar to theUF laser beam, the OCT sample beam 102 passes through the Z-telescope84, is redirected by the X-scan device 86 and by the Y-scan device 88,passes through the objective lens assembly 94 and the patient interface52, and on into the eye 43. Reflections and scatter off of structureswithin the eye provide return beams that retrace back through thepatient interface 52, back through the shared optics 50, back throughthe pickoff/combiner assembly 100, and back into the OCT light sourceand detection device 98. The returning back reflections of the samplebeam 102 are combined with the returning reference portion 104 anddirected into the detector portion of the OCT light source and detectiondevice 98, which generates OCT signals in response to the combinedreturning beams. The generated OCT signals that are in turn interpretedby the control electronics to determine the spatial disposition of thestructures of interest in the patient's eye 43. The generated OCTsignals can also be interpreted by the control electronics to measurethe position and orientation of the patient interface 52, as well as todetermine whether there is liquid disposed between the posterior surfaceof the patient interface lens 96 and the patient's eye 43.

The OCT light source and detection device 98 works on the principle ofmeasuring differences in optical path length between the reference path106 and the sample path. Therefore, different settings of theZ-telescope 84 to change the focus of the UF laser beam do not impactthe length of the sample path for an axially stationary surface in theeye of patient interface volume because the optical path length does notchange as a function of different settings of the Z-telescope 84. Theranging subsystem 46 has an inherent Z range that is related to thelight source and detection scheme, and in the case of frequency domaindetection the Z range is specifically related to the spectrometer, thewavelength, the bandwidth, and the length of the reference path 106. Inthe case of ranging subsystem 46 used in FIG. 3, the Z range isapproximately 4-5 mm in an aqueous environment. Extending this range toat least 20-25 mm involves the adjustment of the path length of thereference path via a stage ZED106 within ranging subsystem 46. Passingthe OCT sample beam 102 through the Z-telescope 84, while not impactingthe sample path length, allows for optimization of the OCT signalstrength. This is accomplished by focusing the OCT sample beam 102 ontothe targeted structure. The focused beam both increases the returnreflected or scattered signal that can be transmitted through the singlemode fiber and increases the spatial resolution due to the reducedextent of the focused beam. The changing of the focus of the sample OCTbeam can be accomplished independently of changing the path length ofthe reference path 106.

Because of the fundamental differences in how the sample beam 102 (e.g.,810 nm to 850 nm wavelengths) and the UF laser pulse beam 66 (e.g., 1020nm to 1050 nm wavelengths) propagate through the shared optics 50 andthe patient interface 52 due to influences such as immersion index,refraction, and aberration, both chromatic and monochromatic, care mustbe taken in analyzing the OCT signal with respect to the UF laser pulsebeam 66 focal location. A calibration or registration procedure as afunction of X, Y, and Z can be conducted in order to match the OCTsignal information to the UF laser pulse beam focus location and also tothe relative to absolute dimensional quantities.

There are many suitable possibilities for the configuration of the OCTinterferometer. For example, alternative suitable configurations includetime and frequency domain approaches, single and dual beam methods,swept source, etc, are described in U.S. Pat. Nos. 5,748,898; 5,748,352;5,459,570; 6,111,645; and 6,053,613.

The system 2 can be set to locate the anterior and posterior surfaces ofthe lens capsule and cornea and ensure that the UF laser pulse beam 66will be focused on the lens capsule and cornea at all points of thedesired opening. Imaging modalities and techniques described herein,such as for example, Optical Coherence Tomography (OCT), and such asPurkinje imaging, Scheimpflug imaging, confocal or nonlinear opticalmicroscopy, fluorescence imaging, ultrasound, structured light, stereoimaging, or other known ophthalmic or medical imaging modalities and/orcombinations thereof may be used to determine the shape, geometry,perimeter, boundaries, and/or 3-dimensional location of the lens andlens capsule and cornea to provide greater precision to the laserfocusing methods, including 2D and 3D patterning. Laser focusing mayalso be accomplished using one or more methods including directobservation of an aiming beam, or other known ophthalmic or medicalimaging modalities and combinations thereof, such as but not limited tothose defined above.

Optical imaging of the cornea, anterior chamber, and lens can beperformed using the same laser and/or the same scanner used to producethe patterns for cutting. Optical imaging can be used to provideinformation about the axial location and shape (and even thickness) ofthe anterior and posterior lens capsule, the boundaries of the cataractnucleus, as well as the depth of the anterior chamber and features ofthe cornea. This information may then be loaded into the laser 3-Dscanning system or used to generate a three dimensionalmodel/representation/image of the cornea, anterior chamber, and lens ofthe eye, and used to define the cutting patterns used in the surgicalprocedure.

Observation of an aim beam can also be used to assist in positioning thefocus point of the UF laser pulse beam 66. Additionally, an aim beamvisible to the unaided eye in lieu of the infrared OCT sample beam 102and the UF laser pulse beam 66 can be helpful with alignment providedthe aim beam accurately represents the infrared beam parameters. Thealignment guidance subsystem 48 is included in the assembly 62 shown inFIG. 3. An aim beam 108 is generated by an aim beam light source 110,such as a laser diode in the 630-650 nm range.

Once the aim beam light source 110 generates the aim beam 108, the aimbeam 108 is transmitted along an aim path 112 to the shared optics 50,where it is redirected by a beam combiner 114. After being redirected bythe beam combiner 114, the aim beam 108 follows a shared path with theUF laser pulse beam 66 through the shared optics 50 and the patientinterface 52. In this way, the aim beam 108 is indicative of thelocation of the UF laser pulse beam 66. The aim beam 108 passes throughthe Z-telescope 84, is redirected by the X-scan device 86 and by theY-scan device 88, passes through the beam combiner 90, passes throughthe objective lens assembly 94 and the patient interface 52, and on intothe patient's eye 43.

The video subsystem 92 is operable to obtain images of the patientinterface and the patient's eye. The video subsystem 92 includes acamera 116, an illumination light source 118, and a beam combiner 120.The video subsystem 92 gathers images that can be used by the controlelectronics 54 for providing pattern centering about or within apredefined structure. The illumination light source 118 can be generallybroadband and incoherent. For example, the light source 118 can includemultiple LEDs. The wavelength of the illumination light source 118 ispreferably in the range of 700 nm to 750 nm, but can be anything that isaccommodated by the beam combiner 90, which combines the light from theillumination light source 118 with the beam path for the UF laser pulsebeam 66, the OCT sample beam 102, and the aim beam 108 (beam combiner 90reflects the video wavelengths while transmitting the OCT and UFwavelengths). The beam combiner 90 may partially transmit the aim beam108 wavelength so that the aim beam 108 can be visible to the camera116. An optional polarization element can be disposed in front of theillumination light source 118 and used to optimize signal. The optionalpolarization element can be, for example, a linear polarizer, a quarterwave plate, a half-wave plate or any combination. An additional optionalanalyzer can be placed in front of the camera. The polarizer analyzercombination can be crossed linear polarizers thereby eliminatingspecular reflections from unwanted surfaces such as the objective lenssurfaces while allowing passage of scattered light from targetedsurfaces such as the intended structures of the eye. The illuminationmay also be in a dark-field configuration such that the illuminationsources are directed to the independent surfaces outside the capturenumerical aperture of the image portion of the video system.Alternatively the illumination may also be in a bright fieldconfiguration. In both the dark and bright field configurations, theillumination light source maybe used as a fixation beam for the patient.The illumination may also be used to illuminate the patient's pupil toenhance the pupil iris boundary to facilitate iris detection and eyetracking. A false color image generated by the near infrared wavelengthor a bandwidth thereof may be acceptable.

The illumination light from the illumination light source 118 istransmitted through the beam combiner 120 to the beam combiner 90. Fromthe beam combiner 90, the illumination light is directed towards thepatient's eye 43 through the objective lens assembly 94 and through thepatient interface 94. The illumination light reflected and scattered offof various structures of the eye 43 and patient interface travel backthrough the patient interface 94, back through the objective lensassembly 94, and back to the beam combiner 90. At the beam combiner 90,the returning light is directed back to the beam combiner 120 where thereturning light is redirected toward the camera 116. The beam combinercan be a cube, plate, or pellicle element. It may also be in the form ofa spider mirror whereby the illumination transmits past the outer extentof the mirror while the image path reflects off the inner reflectingsurface of the mirror. Alternatively, the beam combiner could be in theform of a scraper mirror where the illumination is transmitted through ahole while the image path reflects off of the mirrors reflecting surfacethat lies outside the hole. The camera 116 can be a suitable imagingdevice, for example but not limited to, any silicon based detector arrayof the appropriately sized format. A video lens forms an image onto thecamera's detector array while optical elements provide polarizationcontrol and wavelength filtering respectively. An aperture or irisprovides control of imaging NA and therefore depth of focus and depth offield and resolution. A small aperture provides the advantage of largedepth of field that aids in the patient docking procedure.Alternatively, the illumination and camera paths can be switched.Furthermore, the aim light source 110 can be made to emit infrared lightthat would not be directly visible, but could be captured and displayedusing the video subsystem 92.

FIG. 4 is a simplified schematic diagram illustrating structures thatcan be measured by the laser eye surgery system 2. Structures that canbe measured by the laser eye surgery system 2 (relative to the laser eyesurgery system 2) include, but are not limited to, the patient interfacelens 96, the cornea 122 of the patient's eye 43, and the lens 124 of thepatient's eye 43. Measurements that can be accomplished by the laser eyesurgery system 2 include the distance (CLa) to the anterior surface 125(e.g., apex or in close proximity to the apex) of the patient interfacelens 96 from the objective lens 94, the distance (CLp) to the posteriorsurface 127 (e.g., apex or in close proximity to the apex) of thepatient interface lens 96 from the objective lens 94, the distance (Ca)to the anterior surface 129 (e.g., apex or in close proximity to theapex) of the cornea 122 from the posterior surface 127 of the patientinterface lens 96, the location of points on the anterior surface 129 ofthe cornea 122, the distance (Cp) to the posterior surface 131 (e.g.,apex or in close proximity to the apex) of the cornea 122 from theposterior surface 127 of the patient interface lens 96, the location ofpoints on the posterior surface 131 of the cornea 122, the distance(LTa) to the anterior surface 133 (e.g., apex or in close proximity tothe apex) of the lens 124 from the posterior surface 127 of the patientinterface lens 96, the location of points on the anterior surface 133 ofthe lens 124, the distance (LTp) to the posterior surface 135 (e.g.,apex or in close proximity to the apex) of the lens 124 from theposterior surface 127 of the patient interface lens 96, and the locationof points on the posterior surface 135 of the lens 124. Although notshown in FIG. 4, the iris, pupil, and limbus of the patient's eye 43 canalso be measured/located by the laser eye surgery system 2.

The laser eye surgery system 2 is configured to use the rangingsubsystem 46 and the shared optics 50 to measure/locate the patientinterface lens 96, the cornea 122, the lens 124, the iris, the pupil,and the limbus. The laser eye surgery system 2 can also employ thealignment guidance system 48 to measure/locate the iris, the pupil, andthe limbus. The shared optics 50 is used to control the direction of theOCT sample portion beam 102 emitted from the shared optics 50 toward thepatient interface lens 96. At least a portion of the OCT sample portionbeam 102 continues through the patient interface lens 96 and into thepatient's eye. The OCT sample portion beam 102 is scanned in X direction126 by the X-scan device 86 and in the Y-direction 128 by the Y-scandevice 88. The OCT sample portion beam 102 is also focused ontodifferent focus points in the Z-direction 130 by the Z-telescope 84.Although shown offset in FIG. 4, the Z axis is aligned with the opticalcenterlines of the objective lens 94 and the patient interface lens 96.By selectively setting the length of the reference path 106, thelocation of a detection window 132 in the Z-direction 130 can beselected. A small portion of the OCT sample portion beam 102 reflectsfrom a structure within the detection window 132 and travels backthrough the shared optics 50 and into the OCT light source and detectiondevice 98, where the returning reflected light is analyzed incombination with the returning OCT reference portion beam 104 todetermine the Z-direction distance of the structure from which the smallportion of the OCT sample portion beam 102 was reflected. The determinedZ-direction distance, in combination with the associated X direction andY direction of the emitted OCT sample portion beam 102 as directed bythe X-scan device 86 and the Y-scan device 88, is used to determine theX, Y, and Z coordinates of the structure from which the OCT sampleportion beam 102 was reflected, thereby locating the structure relativeto the laser eye surgery system 2.

In many embodiments, the patient interface lens 96 is part of adisposable assembly that is used for one treatment and then replacedwith a new patient interface lens 96. Variability in the disposable lensassembly, however, may be significant enough to impact the positionalaccuracy of the scanning of the treatment beam 66 and/or the OCT sampleportion beam 102 downstream of the patient interface lens. Accordingly,in many embodiments, the location of the anterior and posterior surfacesof the patient interface lens 96 are measured via the ranging subsystem46 and used to compensate for the characteristics of the specificpatient interface lens 96 used in a treatment.

OCT Scanning Methods

FIG. 5 are simplified diagrams illustrating a method 140 forautomatically generating surface models and curved line models thataccurately represent the spatial disposition of optical surfaces andstructures of the patient's eye 43 relative to the laser eye surgerysystem 2. The method 140 can be practiced using any suitable systems,devices, and acts, such as using any suitable systems, devices, and actsdescribed herein. While the acts of the method 140 are listed in aparticular order, any suitable execution order of the acts can be used.

In act 142, the location and thickness of the patient interface lens 96are measured. For example, the ranging subsystem 46 can be used tomeasure the distance (CLa) to the anterior surface 125 (e.g., apex or inclose proximity to the apex) of the patient interface lens 96 and thedistance (CLp) to the posterior surface 127 (e.g., apex or in closeproximity to the apex) of the patient interface lens 96. The measuredCLa and CLp can be checked by comparison with suitable maximum andminimum acceptable values.

In many embodiments, the patient interface 52 includes a patientinterface lens assembly and a suction ring assembly. The patientinterface lens assembly includes the patient interface lens 96 and isdemountably coupled to the laser eye surgery system 2. In manyembodiments, the suction ring assembly is demountably vacuum coupled tothe patient's eye 43 and is then demountably vacuum coupled to thepatient interface lens assembly. In act 144, the ranging subsystem 46 isused to measure the location of the suction ring assembly. For example,the suction ring assembly can include a reference surface that islocated by the ranging subsystem 46. The measured location of thesuction ring assembly can be checked by comparison with suitable maximumand minimum values.

In act 146, the ranging subsystem 46 is used to verify the presence ofinterface fluid between the posterior surface of the patient interfacelens 96 and the patient's eye 43. For example, the ranging subsystem 46can be used to measure the distance to a reference surface of thesuction ring assembly, which is disposed between the posterior surface127 of the patient interface lens 96 and the patient's eye 43. Due tothe different indexes of refraction of air and the interface fluid, themeasured distance to the reference surface of the suction ring assemblywill differ depending on whether the interface fluid is present ormissing.

In act 148, the ranging subsystem 46 is used to measure the cyclotorsionangle of the patient interface 52 relative to the laser eye surgerysystem 2. The suction ring assembly can include a handle that requiresthat the suction ring assembly be coupled with the patient's eye suchthat the handle can only extend to the side of the patient to avoidinterference between the handle and the patient. The suction ringassembly can also include fiducial features located to be measured bythe ranging subsystem 46 to determine the position and the cyclotorsionangle of the suction ring assembly relative to the laser eye surgerysystem 2. The cyclotorsion angle of the suction ring assembly can bechecked by comparison with suitable maximum and minimum values. Thecyclotorsion angle of the suction ring, in combination with the factthat the handle can only extend to the side of the patient, can be usedto determine which eye the suction ring assembly is coupled to (act150).

In many embodiments, the ranging subsystem 46 is used to measure thespatial disposition of the cornea 122 and the lens 124. For example, inact 152, the ranging subsystem 46 is used to measure the location of thecornea anterior surface 129. In act 154, the ranging subsystem 46 isused to obtain cornea scan data that can be processed to locate thecornea anterior surface 129 and the cornea posterior surface 131. In act156, the cornea scan data is processed to generate a surface model ofthe cornea anterior surface. In act 158, the cornea scan data isprocessed to generate a surface model of the cornea posterior surface131. In act 160, the ranging subsystem 46 is used to measure thelocation of the lens anterior surface 133. In act 162, the rangingsubsystem 46 is used to obtain lens anterior surface scan data that canbe processed to locate the lens anterior surface 133. In act 164, thelens anterior scan data is processed to generate a surface model of thelens anterior surface. In act 166, the ranging subsystem 46 is used tomeasure the location of the lens posterior surface 135. In act 168, theranging subsystem 46 is used to obtain lens posterior surface scan datathat can be processed to locate the lens posterior surface 135. In act170, the lens posterior scan data is processed to generate a surfacemodel of the lens posterior surface. In act 172, scan data obtainedusing the ranging subsystem 46, for example, the lens anterior surfacescan data, is processed to generate a surface model of the iris of thepatient's eye 43. In act 174, a video image of the patient's eye 43 isprocessed to identify the pupil of the patient's eye 43. In act 176, acurved line representing the location of the limbus of the patient's eye43 is generated. For example, the curved line representing the limbuscan be generated by intersecting an oriented plane surface model of theiris and the surface model of the cornea anterior surface. In act 178,the location data, the curved-line models, and the surface models ofstructures of the patient's eye 43 can be checked via comparison withsuitable values and/or ranges of values.

FIG. 5 illustrates method 140 in accordance with embodiments. Manyvariations of the method 140 can be performed in accordance withembodiments. The acts of method 140 may comprise steps. The steps can beperformed in any order, the steps can be removed, added or repeated. Thesteps may comprise sub-steps.

The circuitry of system 2 as described herein, for example the processorof system 2, can be configured with instructions to perform one or moreof the steps of the method 140, and the tangible medium of the processormay embody instructions to perform one or more of the steps of method140. In many embodiments, the tangible medium comprises instructions ofa computer readable memory having instructions of a computer program toperform one or more of the steps of the method 140. Alternatively or incombination, the logic array, such as the field programmable gate arrayas described herein can be programmed to perform one or more of thesteps of method 140. In many embodiments, the processor comprises aplurality of processors and may comprise a plurality of distributedprocessors.

Measuring the Patient Interface Lens

FIG. 6 is a simplified diagram illustrating the measurement of thedistance (CLa) to the anterior apex of the patient interface lens 96from the objective lens 94. FIG. 7 is a simplified diagram illustratingthe measurement of the distance (CLp) to the posterior apex of thepatient interface lens 96 from the objective lens 94. Items representedin FIG. 6 and FIG. 7 include the detection window 132, which has anupper limit at Z_(OCT), the anterior surface 125 of the patientinterface lens 96, the posterior surface 127 of the patient interfacelens 96, a focus depth 180 (Z_(focus)) at which the OCT sample portionbeam 102 is focused by the Z-telescope 84, the cornea 122, and the lens124. Because the surfaces of the patient interface lens 96 generatestrong reflections, the respective focus depth 180 (Z_(focus)) for theOCT sample portion beam 102 is located below the respective surfacebeing measured so as to reduce the amount of light reflected from therespective surface back to the OCT light source and detection device 98.

In many embodiments, the detection window 132 is a real portion of alarger detection window that includes a detection window imaginaryportion. In many embodiments, the upper limit 181 at Z_(OCT) is aboundary surface that separates the detection window real and imaginaryportions. In the described embodiments, the detection window imaginaryportion is disposed between the detection window real portion and thelaser eye surgery system 2. In alternate embodiments, the detectionwindow real portion can be disposed between the detection windowimaginary portion and the laser eye surgery system 2. The use of theterms real portion and imaginary portion refers to the analysis of thereturning sample and reference beams by the OCT light source anddetection device 98.

The scanning strategy used to determine the location of the anterior andposterior surfaces of the patient interface lens 96 will now bedescribed. The variables CLa (actual−measured), CLan (nominal locationfor a population of patient interface lenses 96), CLp (actual−measured),and CLpn (nominal for a population of patient interface lenses 96)represent the physical locations of the anterior and posterior surfaces125, 127 of the patient interface lens 96 referenced to the posteriorsurface of the objective lens 94. Z_(oct) is the location of the firstpixel of the OCT A-scan.

CLp can be used for various suitable purposes. For example, CLp can beused to transform Cartesian coordinates of the OCT point (X, Y,Z_(focus)) to the galvo directives (Xm, Ym and Z1) via a look-up tablefor the Z-telescope 84 (LUT_(zI)). While CLp may not be running variablein a look-up table for the adjustable reference path 106 (LUT_(ZED)),CLp can be used as a parameter to determine the usability range of thelook-up table for the adjustable reference path 106 (LUT_(ZED)). CLa andCLp can be used to transform the absolute Z_(oct) (referenced from theobjective) to the Z_(oct)|CLp (referenced from the patient interfacelens 96).

In order to speed up scheduling and execution of the steps to determineCLa and CLp, some of the tasks required can be performed concurrently.The OCT scans used to determine CLa and CLp cannot occur concurrentlybecause there is only one OCT system. The OCT scan used to determineCLp, however, can be accomplished before the computation of CLa (basedon CLan) is accomplished. Accordingly, a temporary CLp* can be obtainedthat is based on CLan. A subsequent step corrects the temporary CLp*into the real CLp based on the newly computed (and real) CLa.

An example procedure for measuring CLa and CLp begins with using thecorresponding default nominal values (e.g., CLan=21.72 mm, CLpn=33.72mm). A group of A-scans arranged as a small spiral is commanded todetermine the CLa location with:

${Zed}_{commanded} = \frac{{CLan} - \Delta}{2}$Z_(focus)_(CLpn) = CLan + γ − CLpnZ_(l) = LUT_(Zl)(x, y, Z_(focus)_(CLpn), CLp = CLpn)

A is selected and used to offset the top of the OCT detection window 132above CLan such that the OCT detection window is positioned to encompassall expected variations in the actual position of the anterior surface125 of the patient interface lens 96. The factor of two reflects theconfiguration of the adjustable OCT reference path 106 in which a changein Zed_(commanded) results in double the change in length of the OCTreference path 106. The distance y focuses the OCT scan away from thesurface so as to avoid its glare. Z_(focus|) _(CLpn) is referenced toCLpn. This introduces an approximation in the focusing location that hasnot significant implications since the signal from the patient interfacelens is very strong.

Due to Zed location variability, the CLa OCT scan is performed at adifferent Zed (Zed_(commanded)≠Zed_(actual)) so that the OCT scan depthis:

Z _(OCT-actual)(X,Y)=Zed _(actual)*2+n _(water) *LUT _(zed)(X,Y)

The CLa location is computed by taking the median of the transformedpixel position of the surface points as:

${CLa} = {{{Zed}_{actual}*2} + {{Median}\left\lbrack {{n_{water}*{{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)}} + {n_{water}\frac{R_{water}}{511}{Pixel}_{n}}} \right\rbrack}}$

R_(water) is the range of the OCT scan in water. Pixel_(n) is indicativeof the depth of the reflecting structure within the OCT detection window132. The LUT value and the mm to pixel transformation are scaled by thewater index of refraction because the LUT and the OCT range assumedistances in water.

After performing the OCT scan to measure CLa, a group of A-scansarranged as a small spiral is commanded to determine the temporary CLp*location. Note that the actual anterior patient interface lens surface(CLa) may not yet have been calculated (e.g., for scheduling purposes itmay be beneficial to proceed with performing the OCT scan to measure CLpbefore CLa has been calculated) and the approximation CLan is usedinstead. Subsequently, a correction is performed to calculate CLp fromCLp*. Referring to FIG. 7, the OCT scan to measure CLp* is commandedwith:

${Zed}_{commanded} = \frac{\left( {{CLan} + {\left( {{CLpn} - {CLan}} \right)*n_{glass}} - \Delta} \right)}{2}$Z_(focus)_(CLpn) = γZ_(l) = LUT_(OCT  Zl)(x, y, Z_(focus)_(CLpn)=, CLp = CLpn)

Due to Zed variability, the OCT scan to measure CLp* is performed atZed_(actual). Using an assumption that the anterior surface 125 of thepatient interface lens 96 is located at CLan, CLp* can be determinedusing:

$\mspace{20mu} {{Z_{OCT}\left( {0,0} \right)} = {\frac{{2*{Zed}_{actual}} - {CLan}}{N_{glass}} + {CLan}}}$${CLp}^{*} = {{Z_{OCT}\left( {0,0} \right)} + {{Median}\left\lbrack {{\frac{n_{water}}{n_{glass}}*{{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)}} + {\frac{n_{water}}{n_{glass}}\frac{R_{water}}{511}{Pixel}_{n}}} \right\rbrack}}$

Because CLp* is based on the assumption that the anterior surface 125 ofthe patient interface lens 96 is located at CLan, a subsequentcorrection based on the actual position (CLa) of the anterior surface ofthe patient interface lens 96 is performed. Once CLa has beendetermined, CLp can be calculated using:

${CLp} = {\frac{2*{Zed}_{actual}}{N_{glass}} + {{CLa}\left( \frac{N_{glass} - 1}{N_{glass}} \right)} + {{Median}\left\lbrack {{\frac{n_{water}}{n_{glass}}*{{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)}} + {\frac{n_{water}}{n_{glass}}\frac{R_{water}}{511}{Pixel}_{n}}} \right\rbrack}}$${Clp} = {{CLp}^{*} + {\left( \frac{N_{glass} - 1}{N_{glass}} \right)\left( {{Cla} - {Clan}} \right)}}$

Once CLa and CLp have been determined, a new set of variables (Z andZed) can be defined relative to CLp.

${{Zed}@{CLp}} = \frac{{CLa} + {\left( {{CLp} - {CLa}} \right)n_{glass}}}{2}$Zed_(CLp) = Zed − Zed@CLp Z_(CLp) = Z − CLp

Measuring the Suction Ring Assembly

A set of A-scans arranged as spiral whose points are aligned in radiusescan be performed to detect a surface 182 of a suction ring assembly 184depicted in FIG. 8A. By using the ranging subsystem 46 to locate thesurface 182, the x, y center of the suction ring assembly 184 can bedetermined. It can also be used to determine whether the interfaceliquid (e.g., a sterile buffered saline solution (BSS) such as Alcon BSS(Alcon Part Number 351-55005-1) or equivalent) is present between thepatient interface lens 96 and the patient's eye 43. It can also be usedto detect if the suction ring assembly 184 is correctly docked in placerelative to the laser eye surgery system 2. For example, FIG. 8B showsan example location of the surface 182 when the suction ring assembly184 is correctly docked (e.g., surface 182 is at 4.2 mm). In contrast,FIG. 8C shows an example location of the surface 182 when the suctionring assembly 184 is incorrectly docked (e.g., surface 182 is at 5.6mm). FIG. 8D shows an example measured location of the surface 182 whenthe interface liquid is missing from the suction ring assembly 184(e.g., the surface 182 appears to at 3.2 mm due to difference inrefractive index between air and the interface liquid). The x, y centeris used in the determination of the cyclotorsional orientation of thepatient interface.

Cyclotorsion Angle Measurement and Eye (R/L) Type

A set of A-scans arranged as a ring is performed to detect a surface 186of the suction ring assembly 184 depicted in FIG. 8A. The surface 186contains 3 notches at the 0, Pi/2 and Pi locations. The results of theOCT scan are convoluted with a template that is shifted until a bestmatch is achieved. The resulting orientation of the template isindicative of the cyclotorsion angle of the suction ring assembly 184relative to the laser eye surgery system 2. In many embodiments, thesuction ring assembly 184 has a protruding handle that extends sidewaysfrom the suction ring assembly 184. As a result, the suction ringassembly 184 can only be coupled with the patient's eye such that theprotruding handle extends to the side of the patient to avoidinterference between the protruding handle and the patient. Accordingly,the resulting orientation of the template is indicative of which eye thesuction ring assembly 184 is coupled with.

FIG. 8E shows a return signal 188 from the ranging subsystem 46. Thereturn signal 188 exhibits three displaced segments, corresponding tothe three notches at the 0, Pi/2 and Pi locations in the surface 186. Aline 190 represents a best match fit of the template to the surface 186and the three notches at the 0, Pi/2 and Pi locations in the surface186.

Anterior Cornea Prescan

A group of A-scans arranged as a spiral is commanded to determine the zposition of the anterior surface 129 of the cornea 122 (e.g., the apexof the cornea anterior surface 129 on in close proximity to the apex). Aplane can be defined that includes the z position of the anteriorsurface 129 of the cornea 122. The plane can be used during subsequentdetermination of a surface model for the anterior surface 129 of thecornea 122. As illustrated in FIGS. 9A and 9B, the anterior corneaprescan can be commanded with:

${{Zoct}_{commanded}\text{}_{CLp}} = {\frac{{WaterGap}_{\min}}{2} - \delta}$${{Zed}_{commanded}\text{}_{CLp}} = {\left( {\frac{{WaterGap}_{\min}}{2} - \delta} \right)\frac{n_{water}}{2}}$Zfocus_(CLp) = WaterGap_(nom)Z_(l) = LUT_(OCT  Zl)(X, Y, Zfocus_(CLp), CLp)

Due to variations CLp and natural variations in the z position of theanterior surface 129 of the cornea 122, there are a range of possiblepositions of the anterior surface 129 of the cornea 122. For example,FIG. 9A illustrates a minimum gap between the anterior surface 129 ofthe cornea 122 and the posterior surface 127 of the patent interfacelens 96. In contrast, FIG. 9B illustrates a minimum gap between theanterior surface 129 of the cornea 122 and the posterior surface 127 ofthe patent interface lens 96. The OCT detection window 132 is selectedsuch that the anterior cornea surface is detectable in both extremes andwill be detectable in the cases in between. The dotted line 180(Z_(focus)) represents the focusing depth.

As illustrated in FIG. 9A, the OCT detection window 132 is also selectedto position a reflection 192 of the posterior surface 127 of the patientinterface lens 96 above the highest possible location of the anteriorsurface 129 of the cornea 122. This choice leaves the reflection 192 ofthe posterior patient interface lens surface 127 behind by 6 and is 6from the closest the cornea 122 can be. Since the anterior corneasurface 129 is detected from above, the potential presence of thereflection 192 in the OCT detection window 132 does not interfere withthe detection of the cornea anterior surface 129. The usable range ofthis OCT window is:

Z_(min) = 2 * Zoct + δ  (marked  as  a  dotted  black   line)Z_(max) = Zoct + R_(water)  (to  the  end)${{Zoct}_{actual}\text{}_{CLp}\left( {0,0} \right)} = {\left( {{Zed}_{actual}\text{}_{CLp}} \right)\frac{2}{N_{water}}}$

The anterior surface 129 of the cornea 122 is computed by (plane fittingvia) taking the median of the transformed pixel position of the surfacepoints as:

${{A.\; {Cornea}}\mspace{14mu} {Location}}\; = \; {{Zoct}_{actual}_{CLp}{\left( {0,0} \right) + {{Median}\left\lbrack {{{LUT}_{Zed}\left( {X,Y,} \right)} + \frac{R_{water}*{Pixel}_{n}}{511}} \right\rbrack}}}$

If the Cornea Anterior location is not found, assumed values used for asubsequent scan to locate points on the anterior surface 129 of thecornea 122 can be created at:

Cornea Location=Water Gap minimum

Cornea Focus=Water Gap Nominal

In many embodiments, the group of A-scans arranged as a spiral used todetermine the z position of the anterior surface 129 of the cornea 122uses two or more focus depths. For example, FIG. 9C shows an examplegroup of A-scans 194 arranged as a spiral that can be used to locate theanterior surface 129 of the cornea 122. The A-scans 194 include fiveseparate spiral patterns that are each focused at a different depth,with the focus depth of adjacent spiral patterns being separated by 0.5mm. Any suitable number of different focus depths (e.g., 2, 3, 4, 5, 6,7, 8 or more) can be used. Other suitable separation between focusdepths of adjacent patterns (e.g., 0.25 mm, 0.4 mm, 0.6 mm, 0.75 mm) canalso be used. By varying the focus depth, an increase in the resultingsignal can be achieved by increasing the amount of radiation that isreflected from the structure being measured back to the OCT light sourceand detection device 98.

In many embodiments, the group of A-scans arranged as a spiral used todetermine the z position of the anterior surface 129 of the cornea 122is limited in transverse extent so as to limit the number of targetedlocations and concentrate the targeted locations around the likelylocation of the apex of the anterior surface 129 of the cornea 122. Forexample, the group of A-scans arranged as a spiral used to determine thez position of the anterior surface can have a maximum transversedimension of less than 2.0 mm. In a preferred embodiment, the group ofA-scans arranged as a spiral used to determine the z position of theanterior surface can have a maximum transverse dimension of less than1.2 mm (e.g., 1.0 mm as shown in FIG. 9C).

Edge Detection

Each A-scan of the OCT scan of the patient interface lens can besearched for the maximum brightness point. The identified maximums thatare above a threshold can be used to define CLa and CLp.

As discussed herein, the Anterior Cornea prescan uses a series of smallspiral scans with changing focus location as shown in FIG. 9C. A similarprescan approach can also be used to locate the anterior surface of thelens capsule 133 and to locate the posterior surface of the lens capsule135.

In each of the focusing steps in a given prescan, a search for an edgewithin a suitable number of pixels from the focusing location can beperformed. For example, Canny edge detection can be performed withinevery focusing step window to find edges. FIG. 10A shows OCT datadepicting a stepping focus. FIG. 10B shows a view of the OCT data ofFIG. 10A for one focus step. The Canny edge detection convolutes A-scanswith a derivative of a Gaussian. The Kernel is generated using aGaussian first derivative with standard deviation and a number ofstandard deviations. Edge candidates are the maximum or minimum withineach convolution, but are only considered for surface fitting if theyare in absolute value larger than a suitable threshold. FIG. 10C showsoriginal OCT scan data for one focus. FIG. 10D shows a convoluted imagewith Gaussian derivative. And FIG. 10E shows a detected edge 196.

Cornea Scan

A group of A-scans arranged as a spiral can be commanded primarily tolocate points on the anterior and posterior cornea surfaces 129, 131.The spiral can be focused between the two cornea surfaces, according totheir nominal dimensions. A surface model (e.g., a sphere, an ellipsoid)of the anterior surface 129 of the cornea 122 can then be determinedusing points located on the anterior surface 129 of the cornea 122. Thepreviously found location of the anterior surface 129 of the cornea 122can also be used in the determination of the surface model of theanterior surface 129 of the cornea 122. A plane can be fit to thelocation of the posterior corneal surface 131. A surface model (e.g., asphere, an ellipsoid) of the posterior surface 131 of the cornea 122 canbe determined using the points located on the posterior surface of thecornea. The plane fit can also be used in the determination of thesurface model of the posterior surface 131 of the cornea 122. Asillustrated in FIGS. 11A through 11D, the Cornea Scan can be commandedwith:

  Zoct_(commanded)_(CLp) = A. Cornea  Location  − δ$\mspace{20mu} {{{Zed}_{commanded}_{CLp}} = {\left( {{{A.\; {Cornea}}\mspace{14mu} {Location}}\; - \delta} \right)\frac{n_{water}}{2}}}$${{Zfocus}\text{}_{CLp}} = {{{A.\mspace{11mu} {Cornea}}\mspace{20mu} {Focus}} + \frac{{Cornea}\mspace{14mu} {Thickness}_{nom}}{2} + R_{nom} - \sqrt{R_{nom}^{2} - X^{2} - Y^{2}}}$  LUT_(OCT  Zl)(X, Y, Z_(focus)_(CLp), CLp) → X_(m), Y_(m), Z_(L)$\mspace{20mu} {R_{nom} = \frac{{{A.\; {Cornea}}\mspace{14mu} {{Radiu}s}_{nom}} + {{P.\; {Cornea}}\mspace{14mu} {Radius}_{nom}}}{2}}$

FIGS. 11A through 11D show combinations of maximum and minimum anteriorchamber depth and gap between the posterior surface 127 of the patientinterface lens and the patient's eye (“water gap”). FIG. 11A shows theminimum anterior chamber depth with the minimum water gap. FIG. 11Bshows the minimum anterior chamber depth with the maximum water gap.FIG. 11C shows the maximum anterior chamber depth with the minimum watergap. FIG. 11D shows the maximum anterior chamber depth with the maximumwater gap.

A portion of the OCT window can be processed so as to only look for thecorneal anterior and posterior surfaces 129, 131 in likely locations.The processed portion of the OCT window can be located between an upperbounding surface (Zmin) and a lower bounding surface (Zmax). Forexample, the processed portion of the OCT window can be X and Ydependent such as:

Z _(min) =Zoct(X,Y)+R _(min)−√{square root over (R _(min) ² −X ² −Y ²)}

Z _(max) =Zoct(X,Y)+Cornea Thk _(max) +δ+R _(max)−√{square root over (R_(max) ² −X ² −Y ²)}

R _(min) =A. Cornea Radius_(max)

R _(max) =P.Cornea Radius_(min)

The processed window is configured to encompass likely spatialdistributions for the anterior and posterior cornea surfaces 129, 131.Each identified point on the surface of either the cornea anteriorsurface 129 or the cornea posterior surface 131 can be translated fromthe B-Scan image into Cartesian coordinates as:

${{Point}\mspace{20mu} {{Coordinate}\left( {X,Y} \right)}\text{}_{CLp}} = {{\left( {{Zed}_{actual}\text{}_{CLp}} \right)\frac{2}{N_{water}}} + \frac{R_{water}*{Pixel}_{n}}{511} + {{LUT}_{Zed}\left( {X,Y} \right)}}$

Anterior Lens Prescan

A group of A-scans arranged as a spiral can be commanded primarily todetermine the location of the anterior lens surface 133. The group ofA-scans used to determine the location of the anterior lens surface 133can be focused at, for example, the nominal anterior chamber depth. Aplane can be fit to the located anterior lens surface 133. Asillustrated in FIGS. 12A and 12B, the group of A-scans used to determinethe location of the anterior lens surface 133 can be commanded with:

${{Zoct}_{commanded}_{CLp}} = {{{A.\; {Cornea}}\mspace{14mu} {Location}}\; + \frac{{Anterior}\mspace{14mu} {Chamber}_{\min}}{+} - \delta}$${{Zed}_{commanded}_{CLp}} = {\left( {{{A.\; {Cornea}}\mspace{14mu} {Location}} + \frac{{Anterior}\mspace{14mu} {Chamber}_{\min}}{2}\; - \delta} \right)\frac{n_{water}}{2}}$  Zfocus_(CLp) = A. Cornea  Location + Anterior  Chamber_(nom)  LUT_(OCT  Zl)(X, Y, Zfocus_(CLp), CLp) → X_(m), Y_(m), Z_(L)

FIGS. 12A and 12B illustrate minimum and maximum anterior chamber depth,respectively. To exclude reflections from the cornea 122 and theposterior surface 127 of the patient interface lens 96, the processedrange of the OCT detection window can be set to be:

Z _(min) =A. Cornea Location+Anterior Chamber_(nom)−δ

Z _(max)=Min[2*Zoct−δ,Zoct+R _(water)]

The location of the Anterior Lens surface 133 can be calculated using:

${{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}} = {{\left( {{Zed}_{actual}_{CLp}} \right)\frac{2}{N_{water}}} + \frac{\sum\limits_{n}\begin{Bmatrix}{{{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)} +} \\\frac{R_{water}*{Pixel}_{n}}{511}\end{Bmatrix}}{n}}$

If the Anterior Lens surface 133 is not found, assumed values used for asubsequent scan to locate points on the anterior surface 133 of the lens124 can be created at:

A. Lens Location=A. Cornea Location+Anterior Chamber minimum

A. Lens Focus=A. Cornea Location+Anterior Chamber Nominal

In many embodiments, the group of A-scans arranged as a spiral used todetermine the z position of the anterior surface 133 of the lens 124uses two or more focus depths. For example, the example group of A-scans194 shown in FIG. 9C can also be used to locate the anterior surface 133of the lens capsule. Variations discussed above with respect to theexample group of A-scans 194 shown in FIG. 9C can also be applied withregard to the group of A-scans used to locate the anterior surface 133of the lens capsule.

Anterior Lens Scan

A group of A-scans arranged as a spiral can be commanded primarily tolocate points on the anterior lens surfaces 133. The group of A-scansused to locate points on the anterior lens surface 133 can be focused,for example, at the nominal anterior chamber depth. As illustrated inFIGS. 13A and 13B, the group of A-scans used to locate points on theanterior lens surface 133 can be commanded with:

Zoct_(commanded)_(CLp) = A. Lens  Location_(CLp) +R_(water) − 6 δ${{Zed}_{commanded}_{CLp}} = {\left( {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; {{+ R_{water}} - {6\; \delta}}} \right)\frac{n_{water}}{2}}$  Zfocus_(CLp) = A. Lens  Focus_(CLp)  LUT_(OCT  Zl)(X, Y, Zfocus_(CLp), CLp) → X_(m), Y_(m), Z_(L)

FIGS. 13A through 13D illustrate combinations of maximum and minimumanterior chamber depth and maximum and minimum lens thickness. FIG. 13Aillustrates the minimum anterior chamber depth with the minimum lensthickness. FIG. 13B shows the minimum anterior chamber depth with themaximum lens thickness. FIG. 13C shows the maximum anterior chamberdepth with the minimum lens thickness. FIG. 13D shows the maximumanterior chamber depth with the maximum lens thickness.

As illustrated in FIGS. 13A through 13D, the OCT detection window 132 ispositioned below the anterior surface 133 of the lens capsule in allinstances. Accordingly, the OCT data is processed to detect a lensanterior surface reflection 198.

Locations on the anterior surface 133 of the lens 124 can be calculatedusing the inverted scan.

${{Point}\mspace{14mu} {A.\; {Lens}}\text{}_{CLp}\left( {X,Y} \right)} = {{\left( {{Zed}_{actual}_{CLp}} \right)\frac{2}{N_{water}}} + {- R_{water}} + {{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)} + \frac{R_{water}*\left( {511 - {Pixel}_{n}} \right)}{511}}$

Note the media below the reflection of the anterior lens is water, sothat no correction needs to take place.

Posterior Lens Prescan

A group of A-scans arranged as a spiral can be commanded primarily todetermine the location of the posterior lens surface 135. The group ofA-scans used to determine the location of the posterior lens surface 135can be focused below the located anterior surface 133 of the lenscapsule by the nominal thickness of the lens 124. The location of theposterior lens surface 135 can be subsequently fitted with a plane. Asillustrated in FIGS. 14A and 14B, the group of A-scans used to determinethe location of the apex of the posterior lens surface 135 can becommanded with:

${{Zoct}_{commanded}_{CLp}} = {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; {{+ \; {{Lens}\mspace{14mu} {Thickness}_{\max}\frac{N_{{Lens} - \max}}{N_{water}}}} + \delta + {WG}_{nom} + {ACD}_{nom} - {WG}_{\min} - {ACD}_{{mi}n}}}$${{Zed}_{commanded}_{CLp}} = {\left( {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; {{+ {{Lens}\mspace{14mu} {Thickness}_{\max}\frac{N_{{Lens} - \max}}{N_{water}}}} + \delta + {WG}_{nom} + {ACD}_{nom} - {WG}_{\min} - {ACD}_{{mi}n}}} \right)\frac{N_{water}}{2}}$${{{Zfocus}\text{}_{CLp}} = {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; \left. {{+ \; {Lens}}\mspace{14mu} {Thickness}_{nomx}\frac{N_{water}}{N_{{Lens} - {nom}}}\mspace{20mu} {{LUT}_{{OCT}\mspace{11mu} {Zl}}\left( {X,Y,{{Zfocus}_{CLp}},{CLp}} \right)}}\rightarrow X_{m} \right.}},Y_{m},Z_{L}$

FIGS. 14A and 14B illustrate minimum and maximum lens thickness,respectively. The OCT detection window 132 is located below theposterior surface 135 of the lens capsule in all instances so that thelocation of the posterior surface 135 of the lens capsule is determinedusing the inverted scan. Note that the reflection of the anteriorsurface 125 of the patient interface lens 96 is never in the scanwindow.

${{{Location}\mspace{14mu} {A.\; {Lens}}}_{CLp}\left( {X,Y} \right)} = {{{A.\; {lens}}\mspace{14mu} {Loc}} + {\left\lbrack {\left\{ {{\left( {{Zed}_{actual}_{CLp}} \right)\frac{2}{N_{water}}} - R_{water}} \right\} - {{A.\; {lens}}\mspace{14mu} {Loc}}} \right\rbrack \frac{N_{water}}{N_{{Lens} - \max}}} + \frac{\sum\limits_{n}\begin{Bmatrix}{{{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)} +} \\\frac{\frac{R_{air}}{N_{{Lens} - \max}}*\left( {511 - {Pixel}_{n}} \right)}{511}\end{Bmatrix}}{n}}$

In many embodiments, the group of A-scans arranged as a spiral used todetermine the location of the posterior surface 135 of the lens 124 usestwo or more focus depths. For example, a group of A-scans similar to theexample group of A-scans 194 shown in FIG. 9C can also be used to locatethe posterior surface 135 of the lens capsule. Variations discussedabove with respect to the example group of A-scans 194 can also beapplied with regard to the group of A-scans used to locate the posteriorsurface 135 of the lens capsule.

Posterior Lens Scan

A group of A-scans arranged as a spiral can be commanded primarily tolocate points on the posterior lens surface 135. The spiral can befocused at the depth of the posterior surface 135 of the lens capsule.As illustrated in FIG. 15, the scan can be commanded with the same OCTreference path length (same Zed) used to find the posterior lens surfacelocation, but with a more precise focus:

${{Zoct}_{commanded}_{CLp}} = {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; {{+ \; {{Lens}\mspace{14mu} {Thickness}_{\max}\frac{N_{{Lens} - \max}}{N_{water}}}} + \delta}}$${{Zed}_{commanded}_{CLp}} = {\left( {{{A.\; {Lens}}\mspace{14mu} {Location}}_{CLp}\; {{+ {{Lens}\mspace{14mu} {Thickness}_{\max}\frac{N_{{Lens} - \max}}{N_{water}}}} + \delta}} \right)\frac{N_{water}}{2}}$  Zfocus_(CLp) = P. Lens  Location_(CLp)   LUT_(OCT  Zl)(X, Y, Zfocus_(CLp), CLp) → X_(m), Y_(m), Z_(L)

FIG. 15 illustrates the OCT detection window 132 and the focus location(Z_(focus)) for the group of A-scans to locate points on the posteriorlens surface 135. The OCT detection window 132 is located below theposterior surface 135 of the lens capsule in all instances so thatlocations on the posterior portion 135 of the lens capsule aredetermined using the inverted scan. Note that the reflection of theanterior surface 125 of the patient interface lens 96 is not in the scanwindow.

${{Point}\mspace{14mu} {in}\mspace{14mu} {P.\; {Lens}}\text{}_{CLp}\left( {X,Y} \right)} = {{{A.\; {lens}}\mspace{14mu} {{Loc}\left\lbrack {\left\{ {{\left( {{Zed}_{actual}_{CLp}} \right)\frac{2}{N_{water}}} - R_{water}} \right\} - {{A.\; {lens}}\mspace{14mu} {Loc}}} \right\rbrack}\; \frac{N_{water}}{N_{{Lens} - \max}}} + {{LUT}_{Zed}\left( {X_{n},Y_{n}} \right)} + \frac{\frac{R_{air}}{N_{{Lens} - \max}}*\left( {511 - {Pixel}_{n}} \right)}{511}}$

Automated Surface Fitting

In many embodiments, an iterative process is used to analyze the OCTscan data so as to automatically generate surface models for the corneaanterior surface 129, the cornea posterior surface 131, the lensanterior surface 133, and the lens posterior surface 135. The iterativeprocess begins with identifying locations corresponding to a portion ofthe surface in question. Then, an initial surface model is generatedbased on the identified locations corresponding to a portion of thesurface in question. Next, the initial surface model is used to identifyregions of the OCT scan data to be searched for additional points on thesurface in question. The identified additional points are then used toupdate the initial surface model. The iterative process continues untilthe surface model is finalized.

For example, FIGS. 16A through 16D illustrate an iterative process usedto analyze the OCT scan data to automatically generate a surface modelfor the cornea anterior surface 129. The OCT scan that serves to imageand construct the model of the anterior surface 129 of the cornea 122can be focused using the location of the cornea anterior surface 129identified by the cornea anterior prescan and statistical knowledgeabout the cornea anterior radius. A typical cornea anterior scan cancontain in the vicinity of 1000 single A-scans (line scans). Theiterative process to analyze the OCT scan data to construct the surfacemodel of the cornea anterior surface 129 can start by segmenting a smallnumber of the A-scans to detect a set of first locations on the corneaanterior surface 129. The identified location of the cornea anteriorsurface 129 and statistical knowledge of the cornea anterior radius canbe used to identify a first portion of the OCT scan data to process toidentify the first locations. As illustrated in FIG. 16A, the firstlocations 200 on the cornea anterior surface 129 can be used toconstruct a first surface model 202 (e.g., sphere, ellipsoid, conicoid,toroid, etc.) of the cornea anterior surface 129. The first surfacemodel 202 can then be used to identify a second portion of the OCT scandata (a portion of the OCT scan data in which additional locations onthe cornea anterior surface 129 are expected to be located based on thespatial distribution of the first model) to search for additionallocations on the cornea anterior surface 129. For example, FIG. 16Billustrates a set of second locations 204 identified by searching thesecond portion of the OCT scan data. A second surface model 206 of thecornea anterior surface 129 can then be generated based on the locationof the cornea anterior surface, the first locations 200, and the secondlocations 204. The second surface model 206 can then be used to identifya third portion of the OCT scan data (a portion of the scan data inwhich additional locations on the cornea anterior surface 129 areexpected to be located based on the spatial distribution of the secondmodel 206) to search for additional locations on the cornea anteriorsurface 129. For example, FIG. 16C illustrates a set of third locations208 identified by searching the third portion of the OCT scan data. Athird surface model 210 of the cornea anterior surface 129 can then begenerated based on the location of the cornea anterior surface 129, thefirst locations 200, the second locations 204, and the third locations208. The third surface model 210 can then be used to identify a fourthportion of the OCT scan data (a portion of the scan data in whichadditional locations on the cornea anterior surface 129 are expected tobe located based on the spatial distribution of the third model) tosearch for additional locations on the cornea anterior surface 129. Forexample, FIG. 16D illustrates a set of fourth locations 212 identifiedby searching the fourth portion of the OCT scan data. A fourth surfacemodel of the cornea anterior surface 129 can then be generated based onthe location of the cornea anterior surface 129, the first locations200, the second locations 204, the third locations 208, and the fourthlocations 212. While the iterative process is described with four setsof iteratively identified locations, any suitable number of iterationscan be used (e.g., 1, 2, 3, 4, 5, 6 or more). While any suitable surfacemodel can be used (e.g., sphere, ellipsoid, conicoid, toroid, etc.), ina presently preferred embodiment, a specific ellipsoid is fitted to thelocations identified by the iterative process. In a similar manner, theiterative process can be used to analyze the OCT scan data toautomatically generate a surface model for the cornea posterior surface133, the lens anterior surface 131, and/or the lens posterior surface135.

A surface model of the iris can be generated using OCT edge pointsidentified during processing of the OCT scan data to identify locationson the lens anterior surface 133. Specifically, identified OCT edgepoints that do not comply with the lens anterior surface model (such aspoints 216 shown in FIG. 17A) can be selected as potential locations onthe iris for use in generating a surface model of the iris. For example,an oriented plane can be fit to the potential locations and thepotential locations processed to identify a candidate pupil 218 (FIG.17B) by determining the largest circle that can be fit inside thepotential locations.

A video image (FIG. 17C) of the patient's eye 43 from the alignmentguidance system 48 can also be processed either in isolation or usingthe OCT based iris plane and pupil. The video image can be searched foredges using a Canny filter. The search can proceed radially outward fromthe center of the OCT found pupil. Once edges are found, an outlierremoval scheme can be implemented by sequentially fitting an ellipsespecific to the pupil. Edges located away from the pupil can be removed.

The location of the limbus of the patient's eye 43 can be approximatedas the intersection between the cornea posterior surface model and theoriented plane fitted to the iris points. The projected view of thisintersection is an ellipsoid in the x y plane. FIG. 17D shows corneaanterior surface locations 220, iris locations 216, and an intersection222 of the cornea anterior surface model fit to the cornea anteriorsurface locations 220 and the oriented plane fit to the iris locations216.

Composite Images

FIG. 18A shows an axial cross-sectional composite image of a patient'seye.

FIG. 18B shows a corresponding sagittal cross-sectional composite imageof a patient's eye. The composite images include OCT generatedcross-sectional images of the cornea 122, the lens 124, and an iris 224.The composite images also include cross sections of surface models fitto the cornea 122, the lens 124, and the iris 224. The surface modelsinclude a cornea anterior surface model 226, a cornea posterior surfacemodel 228, a lens anterior surface model 230, a lens posterior surfacemodel 232, and an iris surface model 234. The intersection 236 betweenthe cornea anterior surface model 226 and the iris surface model 234 canbe used as to approximate the location of the limbus.

Optical Surface Verification

The optical surface models generated as described herein, as well aslocations measured by the ranging subsystem 46 as described herein, canbe checked relative to expected value ranges to identify when theoptical surface model and/or the measured location falls outside ofexpected and/or allowable ranges. Such checking can be accomplishedrelative to the patient interface lens 96, the location of the corneaanterior surface 129, the cornea anterior and posterior surface models,the location of the lens anterior surface 133, the lens anterior surfacemodel, the location of the lens posterior surface 135, the lensposterior surface model, and manual fits of the anterior and posteriorsurfaces of the cornea and of the lens.

Patient Interface Lens Checks

The computed posterior location of the patient interface lens andthickness can be compared to their nominal design dimension by theinequalities:

|CLp _(computed) −CLp _(Nominal) |>CLp _(Tol)

|T _(Computed) −T _(Nominal) |>T _(Tol)

If any of these inequalities is true, an error message can be sentand/or identification of the optical surfaces of the patient's eye 43can be stopped. Suitable values for CLp_(Nominal) (nominal location ofthe posterior surface of the patient interface lens 43), CLp_(Tol)(allowable deviation of the location of the posterior surface of thepatient interface lens 43), T_(Nominal) (nominal thickness of thepatient interface lens 43), and T_(Tol) (allowable deviation of thethickness of the patient interface lens 43) can be used.

Cornea Anterior Surface Checks

The location of cornea anterior surface 129 can be checked relative tothe treatment space Z axis to ensure that the location of the corneaanterior surface 129 is close to the treatment space Z axis and that thez location of the cornea anterior surface 129 is consistent withsuitable maximum and minimum water gap values.

√{square root over (x _(center) ² +y _(center) ²)}≧XY _(Tol) (e.g., 7.5mm)

Not(Water Gap_(min.)≦Apex_(Center A. cor.)≦Water Gap_(max.))

If any of these inequalities are true, a suitable error message can besent and/or displayed and the cornea anterior location can be set to:

A. Cor _(Loc)=Water Gap_(min.)

A. Cor _(Loc-focus)=Water Gap_(nom.)

Cornea Anterior Surface Model Checks

The anterior cornea surface model (e.g., sphere) can be checked toensure the x, y position of the center of the anterior cornea surfacemodel is suitably close to the z-axis of the treatment space. Thetolerance (XY_(Tol)) allows for some docking induced variation. If thefollowing inequality is true, a suitable error message can be sentand/or displayed.

√{square root over (x _(center) ² +y _(center) ²)}>XY _(Tol) (e.g., 7.5mm)

The anterior cornea radius can be checked to make sure it is consistentwith suitable minimum and maximum radius values. If the followingcondition is true, a suitable error message can be sent and/ordisplayed.

Not(R _(A. cor. min.) ≦R _(A. cor.) ≦R _(A. cor. max.))

The anterior cornea surface location can be checked to make sure it isconsistent with suitable maximum and minimum water gap values. If thefollowing inequality is true, a suitable error message can be sentand/or displayed.

Water Gap_(min.) ≦Z _(Center A. cor.) −R _(A. cor.)≦Water Gap_(max.)

Cornea Posterior Surface Model Checks

The posterior cornea surface model can be checked to ensure the x, yposition of the center of the posterior cornea surface model is suitablyclose to the center of the anterior cornea surface model. The tolerance(CXY_(Tol)) allows for some docking induced variation. If the followinginequality is true, a suitable error message can be sent and/ordisplayed.

√{square root over ((X _(A.Cor) −X _(P.Cor))²+(Y _(A.Cor) −Y_(P.Cor))²)}>CXY _(Tol) (e.g., 7.5 mm)

A radius of the posterior cornea surface model can be checked to makesure it is consistent with suitable minimum and maximum radius values.If the following condition is true, a suitable error message can be sentand/or displayed.

Not(R _(P. cor. min.) ≦R _(P. cor.) ≦R _(P. cor. max.))

The thickness of the cornea 122 can be checked to make sure it isconsistent with suitable maximum and minimum cornea thickness values. Ifthe following inequality is true, a suitable error message can be sentand/or displayed.

Cornea Thickness_(min.) ≦Z _(Center A. cor.) −R _(A. cor.) −A.Cornea_(Apex)≦Cornea Thickness_(max.)

Lens Anterior Surface Checks

The location of the lens anterior surface 133 can be checked to ensurethe x, y position of the lens anterior surface 133 is suitably close thez-axis of the treatment space and that the z location of the lensanterior surface 133 is consistent with the suitable maximum and minimumanterior chamber depth values and suitable maximum and minimum water gapvalues.

√{square root over (x _(center) ² +y _(center) ²)}≧XY _(Tol)

Not(Water Gap_(min.)+AnteriorChamber_(min.)≦Apex_(Center A. Lens.)≦Water Gap_(max.)+AnteriorChamber_(max.))

If any of the following conditions is true, a suitable error message canbe sent and/or displayed and the inverted anterior lens scan can beplaced and focused at

A. Lens_(Loc) =A. Cor _(Loc)+Anterior Chamber_(min).

A. Lens_(Loc-focus) =A. Cor _(Loc)+Anterior Chamber_(max.)

Z _(OCT) =A. Lens_(Loc) +R _(OCT)−δ (e.g., R _(OCT)=4.87 mm, δ=1.5 mm)

Z _(focus) =A. Lens_(Loc-focus) +AD (e.g., AD=0.25 mm)

Lens Anterior Surface Model Check

The lens anterior surface model can be checked to ensure the x, yposition of the center of the lens anterior surface model is suitablyclose to the center of the cornea posterior surface model. If thefollowing inequality is true, a suitable error message can be sentand/or displayed.

√{square root over ((X _(A.Lens) −X _(A. Cor))²+(Y _(A.Lens) −Y_(A. Cor))²)}CXY _(Tol)

The anterior lens radius can be checked to make sure it is consistentwith suitable maximum and minimum radius values. If the followingcondition is true, a suitable error message can be sent and/ordisplayed.

Not(R _(A. lens. min.) ≦R _(A. lens.) ≦R _(A. lens. max.))

The location of the anterior lens surface can be checked to make sure itis consistent with suitable maximum and minimum anterior chamber depths.If the following condition is true, a suitable error message can be sentand/or displayed.

Not(A. Chamber_(min.)≦(Z _(Center A. lens.) −R _(Center A. lens.))−(Z_(Center A. Cor.) −R _(Center A. Cor.))≦A. Chamber_(max.))

OCT Image Processing

Referring back to the assembly 62 illustrated in FIG. 3, in manyembodiments, the OCT light source and detection device 98 employsspectral domain OCT (SDOCT). SDOCT is capable of high-resolution imagingat remarkably high speeds. Approaches for implementing SDOCT includespectrometer-based SDOCT and swept-source SDOCT. The spectral domain OCTmay provide an optical path configured to perform an optical Fouriertransform of the light reflected from the sample object. This Fouriertransformed light signal is provided to the sensor array as Fourierdomain signals measured with the detector. By digitally Fouriertransforming the signals measured with the detector, the optical profileof light reflected from the beam path can be determined. This approachcan allow the detector to measure several wavelengths simultaneously andallows rapid determination of the light intensity profile along the beampath from the tissue sample. However, as the detector measures theintensity of the optically Fourier transformed signal, the digitalFourier transform can produce artifacts in the images.

In spectrometer-based SDOCT, a broadband light source is used togenerate the light transmitted along the sample and reference paths anda spectrometer measures the resulting interference between the returningsample and reference light as a function of wavelength. The broadbandlight source can be, for example, a super-luminescent diode (SLD) ormode-locked laser. FIG. 19 is a simplified schematic diagramillustrating operating aspects of embodiments of the OCT light sourceand detection device 98. A spectral decomposer 238 separates and directsthe superimposed returning sample and reference light 240 toward aphoto-detector array 242 (e.g., a CCD sensor array or line scan sensor)in order to separate the detected light based on wavelength. Thespectral decomposer 238 may comprise one or more of many components, andmay comprise, for example, an optical grating, a prism, or equivalent.In many embodiments, the spectral decomposer comprises one or lensesintroduced into the optical path, in order to focus the spectrallydispersed light on the sensor array, for example. The separated light244 is incident upon sensors of the photo-detector array 242. Thesensors of the photo-detector array 242 are distributed such that eachsensor of the photo-detector array 242 receives a corresponding portionof the separated light 244 for corresponding wavelengths. The data ofthe sensor array can be Fourier transformed to provide an intensityprofile of light reflected back from the tissue along the beam path. Theintensity profile obtained from the Fourier transform of the sensor scancan be referred to as an A-scan. In many embodiments, the resultingspectral data 246 generated by the photo-detector array 242 is rescaledand resampled evenly in k-space, before it is digitally Fouriertransformed to get a depth profile of the imaged sample. A series ofA-scans can be combined to produce a B-scan, which can, for example, bea cross-sectional depth profile of the imaged sample.

In swept-source SDOCT, a narrowband light source and a photo detectorare employed to measure the resulting interference between the sampleand reference light at different wavelengths over time. A swept-sourceSDOCT system can employ a rapidly tunable narrowband laser. In manyembodiments, the output of the narrowband light source is swept linearlyover a total optical bandwidth over a total sweep time and aninterference signal is acquired at evenly spaced wave lengths. Theinterference signal can be acquired using a single detector or dualbalanced detectors to compensate for intensity fluctuations. As theinterference signal is acquired at evenly spaced wavelengths, theinterference signal can be discrete Fourier transformed (DFT) directlyto derive a depth-resolved OCT line scan of the tissue sample beingimaged. Additional details of SDOCT imaging are described in the paperby Zahid Yoqoob, Jigang Wu, and Changhuei Yang, “Spectral domain opticalcoherence tomography: a better OCT imaging stategy”, pages 6-13 inMolecular Imaging, December 2005.

Mirror Image Artifacts

Because the spectrum acquired in both spectrometer-based SDOCT andswept-source SDOCT is a real function, its Fourier transform (FT) issymmetrical with respect to the equal path-length line in the samplebeing imaged. The symmetrical nature of FT produces a mirror imageartifact in the resulting image. As the photodetector can measureintensity of the interfering light but not the phase, the signal fromthe detector is positive for both positive and negative phasevariations. For each A-scan of the image, there exists a location of theA-scan corresponding to the physical location of the tissue at which thelight reflected from the mirror and the tissue have the same opticalpath length. As this location exits for each of the A-scans of theimage, the A-scan images define an equal-path length line of the image.Without knowing the phase difference between the returning sample andreference light, Fourier-domain detection cannot distinguish positiveand negative time delays and therefore produces an OCT image that issymmetrical about the equal path-length line. The symmetrical OCT imageshows the corresponding uncertainty as to whether the image structure isactually disposed anterior to or posterior to the equal path-lengthline.

Referring now to FIG. 20 and FIG. 21, the generation of mirror imageartifacts for a lens capsule 248 is illustrated for different physicallocations of the lens capsule in relation to the equal path-length lineof the OCT measurement system. The equal path-length line is designatedas Zoct in each of the figures. In FIG. 20, Zoct is disposed anterior toand does not intersect the lens capsule 248 such that an imaged portionof the lens capsule 248 is disposed within the detection window 132. Asa result, when sample light from the OCT light source and detectiondevice 98 is reflected from the imaged portion of the lens capsule 248,the Fourier-domain detection employed generates an image that includesthe imaged portion of the lens capsule 248 and a mirror image 250 of theimaged portion of the lens capsule 248. As the measured location of theimaged portion of the lens capsule 248 relative to Zoct is based on theresulting interference between the returning sample and reference lightportions, and the resulting interference is a result of time-delaygenerated phase differences between the returning sample and referencelight portions, the imaged portion of the lens capsule 248 and themirror image 250 are symmetrical about the equal path-length line(Zoct). In the situation illustrated in FIG. 20, where the imagedstructure of interest is contained solely on one side of the equalpath-length line (Zoct), one side of the resulting image can truncated(in this case the top half containing the mirror image 250), therebyleaving the remaining half for image display.

In FIG. 21, the ZED stage and reference mirror of the OCT system areconfigured such that Zoct is located so as to intersect the lens capsule248. Accordingly, the generated mirror image 250 crosses the equalpath-length line (Zoct) and therefore is partially disposed in each ofthe two sides of the resulting image. As such, mere truncation of oneside of the resulting image is insufficient to prevent the display ofall of the mirror image 250.

Mirror image artifacts can be suppressed by, for example, measuring thespectral phase between the returning sample and reference path light andobtaining the complex scattered field whose inverse Fourier transformgenerates an image of the imaged structure without generating a mirrorimage artifact. The measured spectral phase indicates the side of theequal path-length line that the imaged structure is disposed. Suchapproaches for suppressing mirror image artifacts are described in: (1)Erich Gotzinger, Michael Pircher, Rainer A. Leitgeb, and Christoph K.Hitzenberger, “High speed full range complex spectral domain opticalcoherence tomography”, Opt Express. 2005 Jan. 24; 13(2): 583-594; (2)Fercher A F, Leitgeb R, Hitzenberger C K, Sattmann H, Wojtkowski M.Complex spectral interferometry OCT. Proc. SPIE. 1999; 3564:173-178; (3)Wojtkowski M, Kowalczyk A, Leitgeb R, Fercher A F. Full range complexspectral optical coherence tomography technique in eye imaging. Opt.Lett. 2002; 27:1415-1417. [PubMed: 18026464]; and (4) Targowski P,Wojtkowski M, Kowalczyk A, Bajraszewski T, Szkulmowski M, Gorczynska I.Complex spectral OCT in human eye imaging in vivo. Opt. Commun. 2004;229:79-84.

FIG. 22 shows a composite cross-sectional image 252 of an eye that wasassembled from a plurality of A-scans with a range of equal path-lengthline (Zoct) locations. Suppression of mirror image artifacts was used togenerate the composite cross-sectional image 252.

OCT Integration

In the embodiments of the laser eye surgery system 2 illustrated in FIG.2, the ranging subsystem 46 images the eye 43 through both the sharedoptics 50 and the patient interface 52. The ranging subsystem 46,however, can be integrated into the laser eye surgery system 2 in anysuitable manner.

Referring to FIG. 23, the ranging subsystem 46 can be integrated intothe laser eye surgery system 2 downstream of the shared optics 50 so asto image the eye 43 through the patient interface 52. As anotherexample, the ranging subsystem 46 can be integrated into the laser eyesurgery system 2 so as to not image the eye 43 through the patientinterface 52, but can, for example, image the eye 43 through a separatededicated patient interface. In many suitable embodiments of the lasereye surgery system 2, the ranging subsystem 46 has a known ordeterminable spatial disposition(s) relative to the eye 43, therebyallowing the spatial disposition of eye structures measured by theranging subsystem 46 to be used to accurately direct the laser pulsebeam 66 to treat targeted eye structure(s).

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

1-36. (canceled)
 37. A laser eye surgery system, comprising: a cuttinglaser subsystem configured to generate a pulsed laser beam; an opticalcoherence tomography (OCT) imaging subsystem, the OCT imaging subsystemincluding an adjustable reference path length, the OCT imaging subsystemconfigured to produce a detection beam having a plurality of wavelengthssuch that the detection window spans a range of distances relative tothe laser eye surgery system; and control optics operably connected tothe cutting laser subsystem and the OCT imaging subsystem, the controlelectronics programmed to: generate an OCT sample beam; focus the OCTsample beam at a plurality of different locations within the eye, theplurality of different locations include at least two differentdistances from the laser eye surgery system, the different distancesdefining a depth range encompassing an expected variability of distancefrom the laser eye surgery system to an corneal anterior surface, to alens capsule anterior surface, or a lens capsule posterior surface; andprocess returning portions of the sample beam focused at the pluralityof different locations to locate, relative to the laser eye surgerysystem, the corneal anterior surface, the lens capsule anterior surface,or the lens capsule posterior surface.
 38. The system of claim 37,wherein the different locations are positioned at least three differentdistances from the laser eye surgery system.
 39. The system of claim 38,wherein the different locations are located at least four differentdistances from the laser eye surgery system.
 40. The system of claim 39,wherein: the different locations are positioned at least five differentdistances from the laser eye surgery system; and the five differentdistances define four intervening separating distances of between 0.25mm and 0.75 mm.
 41. The system of claim 40, wherein at least one of thefour intervening separating distances is between 0.4 mm and 0.6 mm. 42.The system of claim 37, wherein control electronics are programmed toscan the OCT sample beam in a pattern having a maximum transversedimension of less than 2.0 mm for at least two of the differentdistances.
 43. The system of claim 42, wherein the pattern has a maximumtransverse dimension of less than 1.2 mm for at least two of thedifferent distances.
 44. The system of claim 37, wherein the referencepath length is held constant during said focusing the OCT sample beam ata plurality of different locations within the eye.
 45. The system ofclaim 37, wherein a boundary surface within the detection window dividesthe detection window into a real portion of the detection window and animaginary portion of the detection window, the detection windowimaginary portion being disposed between the laser eye surgery systemand the detection window real portion.
 46. The system of claim 45,further comprising: an interface lens assembly removably mounted to thelaser eye surgery system so as to be disposed between the OCT imagingsubsystem and the eye, the interface lens assembly including aninterface lens having an anterior surface and a posterior surface,wherein the control electronics are further programmed to set thereference path length to position the detection window boundary surfacebetween the interface lens posterior surface and the corneal anteriorsurface such that the interface lens posterior surface is closer to thedetection window boundary surface than the corneal anterior surface whenprocessing returning portions of the sample beam focused at theplurality of different locations to locate the corneal anterior surface.47. The system of claim 45, further comprising: an interface lensassembly removably mounted to the laser eye surgery system so as to bedisposed between the OCT imaging subsystem and the eye, the interfacelens assembly including an interface lens having an anterior surface anda posterior surface, wherein the control electronics are furtherprogrammed to set the reference path length to position the detectionwindow boundary surface between the interface lens posterior surface andthe lens capsule anterior surface such that the interface lens posteriorsurface is further from the detection window boundary surface than thelens capsule anterior surface when processing returning portions of thesample beam focused at the plurality of different locations to locatethe lens capsule anterior surface.
 48. The system of claim 47, whereinthe detection window boundary surface is positioned such that the corneaanterior surface is closer to the detection window boundary surface thanthe lens capsule anterior surface when processing returning portions ofthe sample beam focused at the plurality of different locations tolocate the lens capsule anterior surface.
 49. The system of claim 45,wherein the control electronics are programmed to set the reference pathlength to position the lens capsule posterior surface between thedetection window boundary surface and the lens capsule anterior surfacewhen processing returning portions of the sample beam focused at theplurality of different locations to locate the lens capsule posteriorsurface.
 50. The system of claim 37, further comprising: an interfacelens assembly removably mounted to the laser eye surgery system so as tobe disposed between the OCT imaging subsystem and the eye, the interfacelens assembly including an interface lens having an anterior surface anda posterior surface, wherein the control electronics are furtherprogrammed to use the OCT imaging system to locate the interface lensposterior surface.
 51. The system of claim 50, wherein the controlelectronics are further programmed to use the OCT imaging system tolocate the interface lens anterior surface.
 52. The system of claim 37,further comprising: an interface assembly that is removably mounted tothe laser eye surgery system so as to be disposed between the OCTimaging subsystem and the eye, the interface assembly including two ormore reference features, the method further, wherein the controlelectronics are further programmed to use the OCT imaging subsystem tolocate the reference features relative to the laser eye surgery system;and comparing the OCT based locations of the reference features relativeto predetermined positions of the reference features to determine atleast one of that the interface assembly is properly mounted to thelaser eye surgery system, that the interface assembly is improperlymounted to the laser eye surgery system, that fluid is present in theinterface assembly, that fluid is missing from the interface assembly,an angular orientation of the interface assembly relative to the lasereye surgery system, or whether the interface assembly is coupled with aleft or a right eye of a patient.
 53. The system of claim 52, whereinthe interface assembly comprises: a suction ring assembly that isconfigured to be coupled with the eye and includes the two or morereference features; and an interface lens assembly that includes aninterface lens and couples the suction ring assembly to the laser eyesurgery system.
 54. A laser eye surgery system having an imaging systemfor generating a surface model of an optical surface of an eye, the eyeincluding a cornea having anterior and posterior surfaces, a lenscapsule having anterior and posterior surfaces, an iris, and a limbus,the method comprising: a cutting laser subsystem configured to generatea pulsed laser beam; an optical coherence tomography (OCT) imagingsubsystem, the OCT imaging subsystem including an adjustable referencepath length, the OCT imaging subsystem configured to produce a detectionbeam having a plurality of wavelengths such that the detection windowspans a range of distances relative to the laser eye surgery system; andcontrol optics operably connected to the cutting laser subsystem and theOCT imaging subsystem, the control electronics programmed to: generatean OCT sample beam; process returning portions of the sample beam tolocate a point on the optical surface relative to the laser eye surgerysystem; focus the OCT sample beam within the eye with the length of thereference path set to position the detection window based on thelocation of the point on the optical surface such that the detectionwindow encompasses the optical surface for all expected variations inspatial disposition of the optical surface; process returning portionsof the sample beam so as to detect first locations on the opticalsurface within a first radial distance of the point on the opticalsurface; generate a first surface model of the optical surface based onthe location of the point on the optical surface and the first locationson the optical surface; process returning portions of the sample beam soas to detect second locations on the optical surface beyond the firstradial distance and within a second radial distance from the point onthe optical surface; and generate a second surface model of the opticalsurface based on the location of the point on the optical surface andthe first and second locations on the optical surface.
 55. The system ofclaim 54, wherein the optical surface is the cornea anterior surface,the lens capsule anterior surface, or the lens capsule posteriorsurface.
 56. The system of claim 54, wherein the control electronics arefurther programmed to process returning portions of the sample beam soas to detect second locations comprises generating a search volumedefined by a first upper limit surface and a first lower limit surface,the first upper and lower limit surfaces being offset from the firstsurface model on respective opposing sides of the first surface model,and wherein said processing returning portions of the sample beamfocused at the plurality of different locations so as to detect secondlocations is limited to the search volume.
 57. The system of claim 55,wherein the control electronics are further programmed: processreturning portions of the sample beam so as to detect third locations onthe optical surface beyond the second radial distance and within a thirdradial distance from the point on the optical surface; and generate athird surface model of the optical surface based on the location of thepoint on the optical surface and the first, second, and third locationson the optical surface.
 58. The system of claim 54, wherein the controlelectronics are further programmed: process returning portions of thesample beam so as to detect third locations on the optical surfacebeyond the second radial distance and within a third radial distancefrom the point on the optical surface; and generate a third surfacemodel of the optical surface based on the location of the point on theoptical surface and the first, second, and third locations on theoptical surface.
 59. The system of claim 54, wherein at least one of thefirst and second surface models is an ellipsoid surface model, aspherical surface model, or a conicoid surface model.
 60. The system ofclaim 54, wherein a boundary surface within the detection window dividesthe detection window into a real portion of the detection window and animaginary portion of the detection window, the detection windowimaginary portion being disposed between the laser eye surgery systemand the detection window real portion.
 61. The system of claim 60,wherein: the optical surface is the lens capsule anterior surface; andthe reference path length is set to position the lens capsule anteriorsurface between the detection window boundary surface and the laser eyesurgery system.
 62. The system of claim 60, wherein: the optical surfaceis the lens capsule posterior surface; and the reference path length isset to position the lens capsule posterior surface between the detectionwindow boundary surface and the laser eye surgery system.
 63. The systemof claim 54, wherein the control electronics are further programmed:calculate a transverse distance between an apex of the optical surfaceand a central axis of the laser eye surgery system; compare thecalculated transverse distance to a predetermined acceptable transversedistance value; and inhibit treatment of the eye if the calculatedtransverse distance exceeds the predetermined acceptable transversedistance value.